revset: fix revision filtering in spanset.contains (regression)

The argument is `x` but the variable tested for filtering is `rev`. `rev`
happens to be a revset methods, ... never part of the filtered revs. This
method is now using `rev` for everything.

mercurial/revset.py

@@ -2783,8 +2783,8 b' class spanset(_orderedsetmixin):'
             for r in iterrange:
                 yield r
 
-    def __contains__(self, x):
-        return self._contained(x) and not (self._hiddenrevs and rev in
+    def __contains__(self, rev):
+        return self._contained(rev) and not (self._hiddenrevs and rev in
                 self._hiddenrevs)
 
     def __nonzero__(self):