py3: alias xrange to range in tests/test-fastannotate-revmap.py

xrange is not available on Python 3.

Differential Revision: https://phab.mercurial-scm.org/D4450

tests/test-fastannotate-revmap.py

@@ -3,9 +3,16 b' from __future__ import absolute_import, '
 import os
 import tempfile
 
-from mercurial import util
+from mercurial import (
+    pycompat,
+    util,
+)
+
 from hgext.fastannotate import error, revmap
 
+if pycompat.ispy3:
+    xrange = range
+
 def genhsh(i):
     return chr(i) + b'\0' * 19