pycompat: fix demand import handling of Queue

When demandimport is enabled, simply importing a non existent module does
not trigger ImportError, a property access is necessary.

mercurial/pycompat.py

@@ -1,18 +1,19 b''
 # pycompat.py - portability shim for python 3
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 """Mercurial portability shim for python 3.
 
 This contains aliases to hide python version-specific details from the core.
 """
 
 from __future__ import absolute_import
 
 try:
     import Queue as _queue
+    _queue.Queue
 except ImportError:
     import queue as _queue
 empty = _queue.Empty
 queue = _queue.Queue