py3: use range instead of xrange on py3 in tests/test-filecache.py

xrange is not present on py3.

Differential Revision: https://phab.mercurial-scm.org/D2324

tests/test-filecache.py

@@ -11,11 +11,15 b' from mercurial import ('
     extensions,
     hg,
     localrepo,
+    pycompat,
     ui as uimod,
     util,
     vfs as vfsmod,
 )
 
+if pycompat.ispy3:
+    xrange = range
+
 class fakerepo(object):
     def __init__(self):
         self._filecache = {}