Which mercurial versions are worth testing against

[Marcin Kasperski]

As I finally learned how to use tox to test against various mercurial
versions (*), I contemplate … which versions to test against. Testing
all of them takes a bit too long, so I'd prefer to stick a few most
important versions.

The question is twofold:

- which mercurials are currently really used „in the wild” (distributed
  by popular distros, frequently seen etc)

- which versions introduced most important api changes?


(*) drone.io is fairly cool. First badge:
    https://bitbucket.org/Mekk/mercurial-update_version