revset: use `subset &` in `bookmark`

Speedup, Weeeeeee!

revset  #0: bookmark()
0) wall 0.002240 comb 0.000000 user 0.000000 sys 0.000000 (best of 571)
1) wall 0.000132 comb 0.000000 user 0.000000 sys 0.000000 (best of 14059)

mercurial/revset.py

@@ -468,7 +468,7 b' def bookmark(repo, subset, x):'
         bms = set([repo[r].rev()
                    for r in repo._bookmarks.values()])
     bms -= set([node.nullrev])
-    return subset.filter(bms.__contains__)
+    return subset & bms
 
 def branch(repo, subset, x):
     """``branch(string or set)``