rust-cpython: change license of ref_sharing.rs to MIT
Since we plan to upstream this feature, it's better to continue further
refactoring under the same license as rust-cpython crate.
According to the file history, copyright holders are:
- Raphaël Gomès <rgomes@octobus.net>
- Valentin Gatien-Baron <valentin.gatienbaron@gmail.com>
- Yuya Nishihara <yuya@tcha.org>
$ 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