Add "repo branch" as an alias for "repo branches"

For those of us that are used to typing "git branch".

Signed-off-by: Mike Lockwood <lockwood@android.com>
diff --git a/main.py b/main.py
index a60641d..2cc7e44 100755
--- a/main.py
+++ b/main.py
@@ -59,6 +59,8 @@
   def __init__(self, repodir):
     self.repodir = repodir
     self.commands = all_commands
+    # add 'branch' as an alias for 'branches'
+    all_commands['branch'] = all_commands['branches']
 
   def _Run(self, argv):
     name = None