user-manual: fix rendering of history diagrams

Asciidoc appears to interpret a backslash at the end of a line as
escaping the end-of-line character, which screws up the display of
history diagrams like

 o--o--o
	\
	 o--...

The obvious fix (replacing "\" by "\\") doesn't work.  The only
workaround I've found is to include all such diagrams in a LiteralBlock.
Asciidoc claims that should be equivalent to a literal paragraph, so I
don't understand why the difference--perhaps it's an asciidoc bug.

Cc: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: "J. Bruce Fields" <bfields@citi.umich.edu>

Documentation/user-manual.txt

@@ -437,11 +437,14 @@ We will sometimes represent git history using diagrams like the one
 below.  Commits are shown as "o", and the links between them with
 lines drawn with - / and \.  Time goes left to right:
 
+
+................................................
          o--o--o <-- Branch A
         /
  o--o--o <-- master
         \
          o--o--o <-- Branch B
+................................................
 
 If we need to talk about a particular commit, the character "o" may
 be replaced with another letter or number.
@@ -1928,25 +1931,29 @@ $ git commit
 You have performed no merges into mywork, so it is just a simple linear
 sequence of patches on top of "origin":
 
-
+................................................
  o--o--o <-- origin
         \
          o--o--o <-- mywork
+................................................
 
 Some more interesting work has been done in the upstream project, and
 "origin" has advanced:
 
+................................................
  o--o--O--o--o--o <-- origin
         \
          a--b--c <-- mywork
+................................................
 
 At this point, you could use "pull" to merge your changes back in;
 the result would create a new merge commit, like this:
 
-
+................................................
  o--o--O--o--o--o <-- origin
         \        \
          a--b--c--m <-- mywork
+................................................
 
 However, if you prefer to keep the history in mywork a simple series of
 commits without any merges, you may instead choose to use
@@ -1963,9 +1970,11 @@ point at the latest version of origin, then apply each of the saved
 patches to the new mywork.  The result will look like:
 
 
+................................................
  o--o--O--o--o--o <-- origin
 		 \
 		  a'--b'--c' <-- mywork
+................................................
 
 In the process, it may discover conflicts.  In that case it will stop
 and allow you to fix the conflicts; after fixing conflicts, use "git
@@ -2073,24 +2082,30 @@ The primary problem with rewriting the history of a branch has to do
 with merging.  Suppose somebody fetches your branch and merges it into
 their branch, with a result something like this:
 
+................................................
  o--o--O--o--o--o <-- origin
         \        \
          t--t--t--m <-- their branch:
+................................................
 
 Then suppose you modify the last three commits:
 
+................................................
 	 o--o--o <-- new head of origin
 	/
  o--o--O--o--o--o <-- old head of origin
+................................................
 
 If we examined all this history together in one repository, it will
 look like:
 
+................................................
 	 o--o--o <-- new head of origin
 	/
  o--o--O--o--o--o <-- old head of origin
         \        \
          t--t--t--m <-- their branch:
+................................................
 
 Git has no way of knowing that the new head is an updated version of
 the old head; it treats this situation exactly the same as it would if
@@ -2151,21 +2166,23 @@ commit.  Git calls this process a "fast forward".
 
 A fast forward looks something like this:
 
+................................................
  o--o--o--o <-- old head of the branch
            \
             o--o--o <-- new head of the branch
+................................................
 
 
 In some cases it is possible that the new head will *not* actually be
 a descendant of the old head.  For example, the developer may have
 realized she made a serious mistake, and decided to backtrack,
 resulting in a situation like:
 
+................................................
  o--o--o--o--a--b <-- old head of the branch
            \
             o--o--o <-- new head of the branch
-
-
+................................................
 
 In this case, "git fetch" will fail, and print out a warning.