git-commit: revamp the git-commit semantics.

 - "git commit" without _any_ parameter keeps the traditional
   behaviour.  It commits the current index.

   We commit the whole index even when this form is run from a
   subdirectory.

 - "git commit --include paths..." (or "git commit -i paths...")
   is equivalent to:

   	git update-index --remove paths...
        git commit

 - "git commit paths..." acquires a new semantics.  This is an
   incompatible change that needs user training, which I am
   still a bit reluctant to swallow, but enough people seem to
   have complained that it is confusing to them.  It

   1. refuses to run if $GIT_DIR/MERGE_HEAD exists, and reminds
      trained git users that the traditional semantics now needs
      -i flag.

   2. refuses to run if named paths... are different in HEAD and
      the index (ditto about reminding).  Added paths are OK.

   3. reads HEAD commit into a temporary index file.

   4. updates named paths... from the working tree in this
      temporary index.

   5. does the same updates of the paths... from the working
      tree to the real index.

   6. makes a commit using the temporary index that has the
      current HEAD as the parent, and updates the HEAD with this
      new commit.

 - "git commit --all" can run from a subdirectory, but it updates
   the index with all the modified files and does a whole tree
   commit.

 - In all cases, when the command decides not to create a new
   commit, the index is left as it was before the command is
   run.  This means that the two "git diff" in the following
   sequence:

       $ git diff
       $ git commit -a
       $ git diff

   would show the same diff if you abort the commit process by
   making the commit log message empty.

This commit also introduces much requested --author option.

	$ git commit --author 'A U Thor <author@example.com>'

Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/core-tutorial.txt

@@ -852,7 +852,7 @@ that branch, and do some work there.
 ------------------------------------------------
 $ git checkout mybranch
 $ echo "Work, work, work" >>hello
-$ git commit -m 'Some work.' hello
+$ git commit -m 'Some work.' -i hello
 ------------------------------------------------
 
 Here, we just added another line to `hello`, and we used a shorthand for
@@ -877,7 +877,7 @@ hasn't happened in the `master` branch at all. Then do
 ------------
 $ echo "Play, play, play" >>hello
 $ echo "Lots of fun" >>example
-$ git commit -m 'Some fun.' hello example
+$ git commit -m 'Some fun.' -i hello example
 ------------
 
 since the master branch is obviously in a much better mood.
@@ -942,7 +942,7 @@ Work, work, work
 and once you're happy with your manual merge, just do a
 
 ------------
-$ git commit hello
+$ git commit -i hello
 ------------
 
 which will very loudly warn you that you're now committing a merge

Documentation/git-commit.txt

@@ -8,8 +8,8 @@ git-commit - Record your changes
 SYNOPSIS
 --------
 [verse]
-'git-commit' [-a] [-s] [-v] [(-c | -C) <commit> | -F <file> | -m <msg>]
-	   [-e] [--] <file>...
+'git-commit' [-a] [-i] [-s] [-v] [(-c | -C) <commit> | -F <file> | -m <msg>]
+	   [-e] [--author <author>] [--] <file>...
 
 DESCRIPTION
 -----------
@@ -40,6 +40,10 @@ OPTIONS
 	Take the commit message from the given file.  Use '-' to
 	read the message from the standard input.
 
+--author <author>::
+	Override the author name used in the commit.  Use
+	`A U Thor <author@example.com>` format.
+
 -m <msg>::
 	Use the given <msg> as the commit message.
 
@@ -63,17 +67,66 @@ OPTIONS
 	commit log message unmodified.  This option lets you
 	further edit the message taken from these sources.
 
+-i|--include::
+	Instead of committing only the files specified on the
+	command line, update them in the index file and then
+	commit the whole index.  This is the traditional
+	behaviour.
+
 --::
 	Do not interpret any more arguments as options.
 
 <file>...::
-	Update specified paths in the index file before committing.
-
+	Commit only the files specified on the command line.
+	This format cannot be used during a merge, nor when the
+	index and the latest commit does not match on the
+	specified paths to avoid confusion.
 
 If you make a commit and then found a mistake immediately after
 that, you can recover from it with gitlink:git-reset[1].
 
 
+Discussion
+----------
+
+`git commit` without _any_ parameter commits the tree structure
+recorded by the current index file.  This is a whole-tree commit
+even the command is invoked from a subdirectory.
+
+`git commit --include paths...` is equivalent to
+
+	git update-index --remove paths...
+	git commit
+
+That is, update the specified paths to the index and then commit
+the whole tree.
+
+`git commit paths...` largely bypasses the index file and
+commits only the changes made to the specified paths.  It has
+however several safety valves to prevent confusion.
+
+. It refuses to run during a merge (i.e. when
+  `$GIT_DIR/MERGE_HEAD` exists), and reminds trained git users
+  that the traditional semantics now needs -i flag.
+
+. It refuses to run if named `paths...` are different in HEAD
+  and the index (ditto about reminding).  Added paths are OK.
+  This is because an earlier `git diff` (not `git diff HEAD`)
+  would have shown the differences since the last `git
+  update-index paths...` to the user, and an inexperienced user
+  may mistakenly think that the changes between the index and
+  the HEAD (i.e. earlier changes made before the last `git
+  update-index paths...` was done) are not being committed.
+
+. It reads HEAD commit into a temporary index file, updates the
+  specified `paths...` and makes a commit.  At the same time,
+  the real index file is also updated with the same `paths...`.
+
+`git commit --all` updates the index file with _all_ changes to
+the working tree, and makes a whole-tree commit, regardless of
+which subdirectory the command is invoked in.
+
+
 Author
 ------
 Written by Linus Torvalds <torvalds@osdl.org> and