bookmarks: directly use base dict 'setitem'

The bmstore '__setitem__' method is setting an extra flag that is not needed
during initialization. Skipping the method will allow further cleanup and yield
some speedup as a side effect.

Before:
! wall 0.009120 comb 0.010000 user 0.010000 sys 0.000000 (best of 312)

After:
! wall 0.007874 comb 0.010000 user 0.010000 sys 0.000000 (best of 360)

mercurial/bookmarks.py

@@ -52,6 +52,7 b' class bmstore(dict):'
         self._repo = repo
         nm = repo.changelog.nodemap
         tonode = bin # force local lookup
+        setitem = dict.__setitem__
         try:
             bkfile = _getbkfile(repo)
             for line in bkfile:
@@ -63,7 +64,7 b' class bmstore(dict):'
                     node = tonode(sha)
                     if node in nm:
                         refspec = encoding.tolocal(refspec)
-                        self[refspec] = node
+                        setitem(self, refspec, node)
                 except (TypeError, ValueError):
                     # - bin(...) can raise TypeError
                     # - node in nm can raise ValueError for non-20-bytes entry