_compat: Add implementation of all().

Change-Id: I40b5bf95c2ae08776a1a7383be4025e2628d65ba

dulwich/_compat.py

@@ -136,6 +136,20 @@ except ImportError:
                 return
 
 
+try:
+    all = all
+except NameError:
+    # Implementation of permutations from Python 2.6 documentation:
+    # http://docs.python.org/2.6/library/functions.html#all
+    # Copyright (c) 2001-2010 Python Software Foundation; All Rights Reserved
+    # Licensed under the Python Software Foundation License.
+    def all(iterable):
+        for element in iterable:
+            if not element:
+                return False
+        return True
+
+
 try:
     from collections import namedtuple
 except ImportError: