bisect: add "git bisect help" subcommand to get a long usage string

Users are not often aware of the fact that "git bisect -h" can give
them a long usage description, as "git bisect" seems to accept only
dashless subcommands like "start", "good", ...

That's why this patch adds a "git bisect help" subcommand that just
calls "git bisect -h". This new subcommand is also fully documented
in the short usage string (that "git bisect" gives), in the long
usage string and in the man page (that "git help bisect" gives).

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-bisect.txt

@@ -15,6 +15,7 @@ DESCRIPTION
 The command takes various subcommands, and different options depending
 on the subcommand:
 
+ git bisect help
  git bisect start [<bad> [<good>...]] [--] [<paths>...]
  git bisect bad [<rev>]
  git bisect good [<rev>...]
@@ -29,6 +30,12 @@ This command uses 'git-rev-list --bisect' option to help drive the
 binary search process to find which change introduced a bug, given an
 old "good" commit object name and a later "bad" commit object name.
 
+Getting help
+~~~~~~~~~~~~
+
+Use "git bisect" to get a short usage description, and "git bisect
+help" or "git bisect -h" to get a long usage description.
+
 Basic bisect commands: start, bad, good
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

git-bisect.sh

@@ -1,7 +1,9 @@
 #!/bin/sh
 
-USAGE='[start|bad|good|skip|next|reset|visualize|replay|log|run]'
-LONG_USAGE='git bisect start [<bad> [<good>...]] [--] [<pathspec>...]
+USAGE='[help|start|bad|good|skip|next|reset|visualize|replay|log|run]'
+LONG_USAGE='git bisect help
+        print this long help message.
+git bisect start [<bad> [<good>...]] [--] [<pathspec>...]
         reset bisect state and start bisection.
 git bisect bad [<rev>]
         mark <rev> a known-bad revision.
@@ -20,7 +22,9 @@ git bisect replay <logfile>
 git bisect log
         show bisect log.
 git bisect run <cmd>...
-        use <cmd>... to automatically bisect.'
+        use <cmd>... to automatically bisect.
+
+Please use "git help bisect" to get the full man page.'
 
 OPTIONS_SPEC=
 . git-sh-setup
@@ -465,6 +469,8 @@ case "$#" in
     cmd="$1"
     shift
     case "$cmd" in
+    help)
+        git bisect -h ;;
     start)
         bisect_start "$@" ;;
     bad|good|skip)