localrepo: fastpath access to "."

"." is just an alias for `p1(wdir())`, let us handle it that way.

Differential Revision: https://phab.mercurial-scm.org/D7494

mercurial/localrepo.py

@@ -1543,6 +1543,9 b' class localrepository(object):'
             pair = (rev, node)
             quick[rev] = pair
             quick[node] = pair
+        p1node = self.dirstate.p1()
+        if p1node != nullid:
+            quick[b'.'] = quick[p1node]
         return quick
 
     @unfilteredmethod