manifest.walk: use return instead of StopIteration in generator

Using "return" within a generator is supposedly more Pythonic than
raising StopIteration.

mercurial/manifest.py

@@ -228,7 +228,7 b' class manifestdict(object):'
         if fset and not match.anypats() and util.all(fn in self for fn in fset):
             for fn in sorted(fset):
                 yield fn
-            raise StopIteration
+            return
 
         for fn in self:
             if fn in fset: