Documentation: link to gitrevisions rather than git-rev-parse

Currently, whenever we need documentation for revisions and ranges, we
link to the git-rev-parse man page, i.e. a plumbing man page, which has
this along with the documentation of all rev-parse modes.

Link to the new gitrevisions man page instead in all cases except
- when the actual git-rev-parse command is referred to or
- in very technical context (git-send-pack).

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/gitcore-tutorial.txt

@@ -971,7 +971,7 @@ commits from the master branch.  The string inside brackets
 before the commit log message is a short name you can use to
 name the commit.  In the above example, 'master' and 'mybranch'
 are branch heads.  'master^' is the first parent of 'master'
-branch head.  Please see linkgit:git-rev-parse[1] if you want to
+branch head.  Please see linkgit:gitrevisions[1] if you want to
 see more complex cases.
 
 [NOTE]