Ignore warning when importing pkg_resources

On Debian Jessie we get a PendingDeprecationWarning which we now see
since the log is init'ed earlier.

qutebrowser/utils/qtutils.py

@@ -33,11 +33,17 @@ import sys
 import operator
 import contextlib
 
-import pkg_resources
 from PyQt5.QtCore import (qVersion, QEventLoop, QDataStream, QByteArray,
                           QIODevice, QSaveFile)
 from PyQt5.QtWidgets import QApplication
 
+from qutebrowser.utils import log
+
+with log.ignore_py_warnings(category=PendingDeprecationWarning, module='imp'):
+    # This imports 'imp' and gives us a PendingDeprecationWarning on
+    # Debian Jessie.
+    import pkg_resources
+
 
 MAXVALS = {
     'int': 2 ** 31 - 1,