manifest: make copy logic local to copy()

The optional arguments to the manfifestdict constructor are only used
by copy(), so assign the fields from that method instead so it's clear
that the arguments are not used for anything else.

mercurial/manifest.py

@@ -10,13 +10,8 b' import mdiff, parsers, error, revlog, ut'
 import array, struct
 
 class manifestdict(dict):
-    def __init__(self, mapping=None, flags=None):
-        if mapping is None:
-            mapping = {}
-        if flags is None:
-            flags = {}
-        dict.__init__(self, mapping)
-        self._flags = flags
+    def __init__(self):
+        self._flags = {}
     def __setitem__(self, k, v):
         assert v is not None
         dict.__setitem__(self, k, v)
@@ -26,7 +21,10 b' class manifestdict(dict):'
         """Set the flags (symlink, executable) for path f."""
         self._flags[f] = flags
     def copy(self):
-        return manifestdict(self, dict.copy(self._flags))
+        copy = manifestdict()
+        dict.__init__(copy, self)
+        copy._flags = dict.copy(self._flags)
+        return copy
     def intersectfiles(self, files):
         '''make a new manifestdict with the intersection of self with files