revset: optimize stringset when subset == entire repo

if range(len(repo)) is passed to stringset and x is a valid rev
(checked before) then x is guaranteed to be in subset, we can check
for that by comparing the lengths of the sets

mercurial/revset.py

@@ -123,7 +123,7 b' def stringset(repo, subset, x):'
     x = repo[x].rev()
     if x == -1 and len(subset) == len(repo):
         return [-1]
-    if x in subset:
+    if len(subset) == len(repo) or x in subset:
         return [x]
     return []