Support msysgit with Chromium.

First step to remove cygwin dependencies. This will remove dependencies with zcsh and allow python scripts to be executed as hooks.

BUG=70550, 70549
TEST=checkout chrome with git, use git cl to upload a cl, revise a cl, commit a cl.

Review URL: http://codereview.chromium.org/6369012

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@76232 0039d316-1c4b-4281-b951-d872f2087c98

update_depot_tools

@@ -46,7 +46,7 @@ then
   test_git_svn
   # work around a git-svn --quiet bug
   OUTPUT=`git svn rebase -q -q`
-  if [[ ! "$OUTPUT" =~ Current.branch ]]; then
+  if [[ ! "$OUTPUT" == *Current.branch* ]]; then
     echo $OUTPUT
   fi
   cd - > /dev/null