Decode bytes before using os.path.join

Otherwise it will raise TypeError when trying to join str() and bytes() instance 
in python-3.3.

Fixes #654
Closes #655

powerline/lib/vcs/git.py

@@ -1,6 +1,9 @@
 # vim:fileencoding=utf-8:noet
 
+from __future__ import (unicode_literals, absolute_import, print_function)
+
 import os
+import sys
 import re
 
 from powerline.lib.vcs import get_branch_name as _get_branch_name, get_file_status
@@ -26,7 +29,7 @@ def git_directory(directory):
 	if os.path.isfile(path):
 		with open(path, 'rb') as f:
 			raw = f.read().partition(b':')[2].strip()
-			return os.path.abspath(os.path.join(directory, raw))
+			return os.path.abspath(os.path.join(directory, raw.decode(sys.getfilesystemencoding() or 'utf-8')))
 	else:
 		return path