urllibcompat: new library to help abstract out some python3 urllib2 stuff

Doing a new file instead of pycompat because I'm starting to feel like
pycompat is getting a little enormous in terms of scope.

Differential Revision: https://phab.mercurial-scm.org/D890

mercurial/urllibcompat.py

@@ -0,0 +1,42 b''
+# urllibcompat.py - adapters to ease using urllib2 on Py2 and urllib on Py3
+#
+# Copyright 2017 Google, Inc.
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+from __future__ import absolute_import
+
+from . import pycompat
+
+if pycompat.ispy3:
+
+    def getfullurl(req):
+        return req.full_url
+
+    def gethost(req):
+        return req.host
+
+    def getselector(req):
+        return req.selector
+
+    def getdata(req):
+        return req.data
+
+    def hasdata(req):
+        return req.data is not None
+else:
+
+    def gethost(req):
+        return req.get_host()
+
+    def getselector(req):
+        return req.get_selector()
+
+    def getfullurl(req):
+        return req.get_full_url()
+
+    def getdata(req):
+        return req.get_data()
+
+    def hasdata(req):
+        return req.has_data()