py3: add PY23() macro to switch string literal depending on python version
I have no better idea to work around the bytes-unicode divergence of
Py_BuildValue(). Maybe we can write a code transformer for C extensions? :)
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state