Pruning all closed branches by default
This is a follow-up to #93, for which we decided that pruning closed branches that had already been pushed all the way to GitLab should not magically disappear at the first unrelated push would have been a break in backwards compatibility, and hence not suitable for Heptapod 0.6.1
In Heptappod 0.7.0, as promised then, we'll prune all closed branches by default. Users can still use
[experimental]
hg-git.prune-previously-closed-branches = yes
to get back to Heptapod 0.6 behaviour