util: use fakebuffer as buffer in py3k

There's no buffer type in py3k, util.py has a function, called
fakebuffer, that implements a similar API. This patch implements
fakebuffer as a memoryview wrapper in py3k.

mercurial/util.py

@@ -38,8 +38,12 b' def _fastsha1(s):'
 
 import __builtin__
 
-def fakebuffer(sliceable, offset=0):
-    return sliceable[offset:]
+if sys.version_info[0] < 3:
+    def fakebuffer(sliceable, offset=0):
+        return sliceable[offset:]
+else:
+    def fakebuffer(sliceable, offset=0):
+        return memoryview(sliceable)[offset:]
 try:
     buffer
 except NameError: