scmutil: make function name bytes in class filecache

func.__name__ returns unicodes and this leads to keyerror when we try
to do filecache[''] by passing bytes.

mercurial/scmutil.py

@@ -885,7 +885,7 b' class filecache(object):'
 
     def __call__(self, func):
         self.func = func
-        self.name = func.__name__
+        self.name = func.__name__.encode('ascii')
         return self
 
     def __get__(self, obj, type=None):