localrepo: iterate over manifest key/value pairs in status

localrepo: iterate over manifest key/value pairs in status

This saves us a couple of dict lookups in the common case, and improves
the performance of the status method by 5% (measured with util.timed)
in a repo with a large manifest.

--- a/mercurial/localrepo.py	Thu Feb 21 12:55:39 2013 -0800
+++ b/mercurial/localrepo.py	Fri Feb 22 10:05:22 2013 -0800
@@ -1532,12 +1532,12 @@
 
             modified, added, clean = [], [], []
             withflags = mf1.withflags() | mf2.withflags()
-            for fn in mf2:
+            for fn, mf2node in mf2.iteritems():
                 if fn in mf1:
                     if (fn not in deleted and
                         ((fn in withflags and mf1.flags(fn) != mf2.flags(fn)) or
-                         (mf1[fn] != mf2[fn] and
-                          (mf2[fn] or ctx1[fn].cmp(ctx2[fn]))))):
+                         (mf1[fn] != mf2node and
+                          (mf2node or ctx1[fn].cmp(ctx2[fn]))))):
                         modified.append(fn)
                     elif listclean:
                         clean.append(fn)