revset: do less lookup during spanset.__contains__

Attribute lookup is slow in python. So this version is going to be a bit
faster. This does not have a visible impact since the rest of the stack is much
slower but this shaves the yak a few extra nanometers.

Moreover the new version is more readable so it worth doing this change for code
quality purpose.

This optimisation was approved by a core python dev.

mercurial/revset.py

@@ -2793,9 +2793,11 @@ class _spanset(_orderedsetmixin):
                 yield r
 
     def __contains__(self, rev):
-        return (((self._end < rev <= self._start)
-                  or (self._start <= rev < self._end))
-                and not (self._hiddenrevs and rev in self._hiddenrevs))
+        start = self._start
+        end = self._end
+        hidden = self._hiddenrevs
+        return (((end < rev <= start) or (start <= rev and rev < end))
+                and not (hidden and rev in hidden))
 
     def __nonzero__(self):
         for r in self: