pyflakes: use pycompat.pickles to prevent error

The pyflakes in my test box complain about pickle in pycompat.

  mercurial/pycompat.py:17: 'pickle' imported but unused

mercurial/pycompat.py

@@ -1,129 +1,130
 # 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 cPickle as pickle
     pickle.dumps
 except ImportError:
     import pickle
+    pickle.dumps # silence pyflakes
 
 try:
     import cStringIO as io
     stringio = io.StringIO
 except ImportError:
     import io
     stringio = io.StringIO
 
 try:
     import Queue as _queue
     _queue.Queue
 except ImportError:
     import queue as _queue
 empty = _queue.Empty
 queue = _queue.Queue
 
 class _pycompatstub(object):
     pass
 
 def _alias(alias, origin, items):
     """ populate a _pycompatstub
 
     copies items from origin to alias
     """
     def hgcase(item):
         return item.replace('_', '').lower()
     for item in items:
         try:
             setattr(alias, hgcase(item), getattr(origin, item))
         except AttributeError:
             pass
 
 urlreq = _pycompatstub()
 urlerr = _pycompatstub()
 try:
     import urllib2
     import urllib
     _alias(urlreq, urllib, (
         "addclosehook",
         "addinfourl",
         "ftpwrapper",
         "pathname2url",
         "quote",
         "splitattr",
         "splitpasswd",
         "splitport",
         "splituser",
         "unquote",
         "url2pathname",
         "urlencode",
         "urlencode",
     ))
     _alias(urlreq, urllib2, (
         "AbstractHTTPHandler",
         "BaseHandler",
         "build_opener",
         "FileHandler",
         "FTPHandler",
         "HTTPBasicAuthHandler",
         "HTTPDigestAuthHandler",
         "HTTPHandler",
         "HTTPPasswordMgrWithDefaultRealm",
         "HTTPSHandler",
         "install_opener",
         "ProxyHandler",
         "Request",
         "urlopen",
     ))
     _alias(urlerr, urllib2, (
         "HTTPError",
         "URLError",
     ))
 
 except ImportError:
     import urllib.request
     _alias(urlreq, urllib.request, (
         "AbstractHTTPHandler",
         "addclosehook",
         "addinfourl",
         "BaseHandler",
         "build_opener",
         "FileHandler",
         "FTPHandler",
         "ftpwrapper",
         "HTTPHandler",
         "HTTPSHandler",
         "install_opener",
         "pathname2url",
         "HTTPBasicAuthHandler",
         "HTTPDigestAuthHandler",
         "ProxyHandler",
         "quote",
         "Request",
         "splitattr",
         "splitpasswd",
         "splitport",
         "splituser",
         "unquote",
         "url2pathname",
         "urlopen",
     ))
     import urllib.error
     _alias(urlerr, urllib.error, (
         "HTTPError",
         "URLError",
     ))
 
 try:
     xrange
 except NameError:
     import builtins
     builtins.xrange = range