mercurial: use pure Python module policy on Python 3
The C extensions don't yet work with Python 3. Let's minimize the
work required to get Mercurial running on Python 3 by always using
the pure Python module policy on Python 3.
#require serve killdaemons
#if windows
$ hg clone http://localhost:$HGPORT/ copy
abort: * (glob)
[255]
#else
$ hg clone http://localhost:$HGPORT/ copy
abort: error: Connection refused
[255]
#endif
$ test -d copy
[1]
$ python "$TESTDIR/dumbhttp.py" -p $HGPORT --pid dumb.pid
$ cat dumb.pid >> $DAEMON_PIDS
$ hg clone http://localhost:$HGPORT/foo copy2
abort: HTTP Error 404: * (glob)
[255]
$ killdaemons.py