Handle Windows line endings when reading binary files

Without this change, '.git\HEAD' files, for examples, are sometime
read incorrectly resulting in the current branch to be reset to
"master" when running a "repo init -b xxx" on an already initialized
repository.

Change-Id: I48c7ef85ff81626edf156914329a560e14252f2a

git_refs.py

@@ -139,7 +139,7 @@ class GitRefs(object):
 
   def _ReadLoose1(self, path, name):
     try:
-      fd = open(path, 'rb')
+      fd = open(path)
     except IOError:
       return