git checkout: add -t alias for --track

Signed-off-by: Miklos Vajna <vmiklos@frugalware.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-checkout.txt

@@ -47,7 +47,7 @@ OPTIONS
 	by linkgit:git-check-ref-format[1].  Some of these checks
 	may restrict the characters allowed in a branch name.
 
---track::
+-t, --track::
 	When creating a new branch, set up configuration so that git-pull
 	will automatically retrieve data from the start point, which must be
 	a branch. Use this if you always pull from the same upstream branch

builtin-checkout.c

@@ -504,7 +504,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		OPT__QUIET(&opts.quiet),
 		OPT_STRING('b', NULL, &opts.new_branch, "new branch", "branch"),
 		OPT_BOOLEAN('l', NULL, &opts.new_branch_log, "log for new branch"),
-		OPT_SET_INT( 0 , "track",  &opts.track, "track",
+		OPT_SET_INT('t', "track",  &opts.track, "track",
 			BRANCH_TRACK_EXPLICIT),
 		OPT_BOOLEAN('f', NULL, &opts.force, "force"),
 		OPT_BOOLEAN('m', NULL, &opts.merge, "merge"),