Fix git branch parsing.

In git version 2.4 the git branch command prints "* (HEAD detached at"
or "* (HEAD detached from" instead of "* (detached from". Adjust the parsing to make our tests
still work with git 2.4.

BUG=487172

Review URL: https://codereview.chromium.org/1162763003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@295578 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/git_common.py b/git_common.py
index 6b21050..a01f8e5 100644
--- a/git_common.py
+++ b/git_common.py
@@ -293,7 +293,7 @@
 
 
 def branches(*args):
-  NO_BRANCH = ('* (no branch', '* (detached from ')
+  NO_BRANCH = ('* (no branch', '* (detached', '* (HEAD detached')
 
   key = 'depot-tools.branch-limit'
   limit = 20