revset: stop using a baseset instead of a plain list in _revsbetween

The function internal code needs a list. Lets use a list.

mercurial/revset.py

@@ -78,7 +78,7 b' def _revsbetween(repo, roots, heads):'
     if not roots:
         return baseset([])
     parentrevs = repo.changelog.parentrevs
-    visit = baseset(heads)
+    visit = list(heads)
     reachable = set()
     seen = {}
     minroot = min(roots)