status: make 'hg status --rev' faster when there are deleted files

In order not to avoid listing files as both added and deleted, for
example, we check for every file in the manifest if it is in the
_list_ of deleted files. This can get quite slow when there are many
deleted files. Change it to a set to make the containment check
faster. On a somewhat contrived example of the Mozilla repo with the
entire testing/ directory deleted (~14k files), this makes
'hg status --rev .^' go from 26s to 2s.

mercurial/context.py

@@ -121,10 +121,11 b' class basectx(object):'
 
         modified, added, clean = [], [], []
         deleted, unknown, ignored = s[3], s[4], s[5]
+        deletedset = set(deleted)
         withflags = mf1.withflags() | mf2.withflags()
         for fn, mf2node in mf2.iteritems():
             if fn in mf1:
-                if (fn not in deleted and
+                if (fn not in deletedset and
                     ((fn in withflags and mf1.flags(fn) != mf2.flags(fn)) or
                      (mf1[fn] != mf2node and
                       (mf2node or self[fn].cmp(other[fn]))))):
@@ -132,7 +133,7 b' class basectx(object):'
                 elif listclean:
                     clean.append(fn)
                 del mf1[fn]
-            elif fn not in deleted:
+            elif fn not in deletedset:
                 added.append(fn)
         removed = mf1.keys()
         if removed: