Mercurial 5.1 released

[Augie Fackler]

Please update your packaged builds, thanks.

Based on the current rate of Python3 improvement and some other developments on tooling, I'm hoping that 5.2 will be a Python3-first release. Python2 will definitely still work then, but I expect "how fast do we drop Python 2" to be a topic at the sprint, and will try to remember to surface any decisions made there to this group. If you'd like to attend the sprint in NYC, please update the 5.2Sprint wiki page.

Thanks!