PERF: Avoid sorting twice in intersection of numeric MultiIndex

Author: Jean-Francois Zinque

pandas/core/indexes/multi.py

@@ -3321,6 +3321,7 @@ def intersection(self, other, sort=False):
         if self.is_monotonic and other.is_monotonic:
             try:
                 uniq_tuples = self._inner_indexer(lvals, rvals)[0]
+                sort = False  # uniq_tuples is already sorted
             except TypeError:
                 pass