log: use an exact matcher for --patch --follow

log: use an exact matcher for --patch --follow

The arguments to log --patch --follow are expected to be exact paths.

This will be used to make manifest filtering for these cases more efficient in
upcoming patches.

--- a/mercurial/cmdutil.py	Wed Jul 16 17:35:04 2014 -0500
+++ b/mercurial/cmdutil.py	Sat Jul 12 18:31:18 2014 -0700
@@ -1499,7 +1499,6 @@
     fcache = {}
     fcacheready = [False]
     pctx = repo['.']
-    wctx = repo[None]
 
     def populate():
         for fn in files:
@@ -1512,7 +1511,7 @@
             # Lazy initialization
             fcacheready[0] = True
             populate()
-        return scmutil.match(wctx, fcache.get(rev, []), default='path')
+        return scmutil.matchfiles(repo, fcache.get(rev, []))
 
     return filematcher