dirstate: avoid use of zip on big lists

In a clean working directory containing 170,000 tracked files, this
improves performance of "hg --time diff" from 1.69 seconds to 1.43.

This idea is due to Siddharth Agarwal.

mercurial/dirstate.py

@@ -696,8 +696,9 b' class dirstate(object):'
         # step 3: report unseen items in the dmap hash
         if not skipstep3 and not exact:
             visit = sorted([f for f in dmap if f not in results and matchfn(f)])
-            for nf, st in zip(visit, util.statfiles([join(i) for i in visit])):
-                results[nf] = st
+            nf = iter(visit).next
+            for st in util.statfiles([join(i) for i in visit]):
+                results[nf()] = st
         for s in subrepos:
             del results[s]
         del results['.hg']