rebase, revlog: use set(x) instead of set(x.keys())

The latter is both unnecessary and slower.

hgext/rebase.py

@@ -128,8 +128,7 b' def rebase(ui, repo, **opts):'
 
         if not keepf:
             # Remove no more useful revisions
-            if (set(repo.changelog.descendants(min(state)))
-                                                    - set(state.keys())):
+            if set(repo.changelog.descendants(min(state))) - set(state):
                 ui.warn(_("warning: new changesets detected on source branch, "
                                                         "not stripping\n"))
             else:

mercurial/revlog.py

@@ -678,7 +678,7 b' class revlog(object):'
             # find from roots.
             heads = dict.fromkeys(heads, 0)
             # Start at the top and keep marking parents until we're done.
-            nodestotag = set(heads.keys())
+            nodestotag = set(heads)
             # Remember where the top was so we can use it as a limit later.
             highestrev = max([self.rev(n) for n in nodestotag])
             while nodestotag: