destmerge: improve topic head computation and handling
This rework get use two benefits:
- heads are now computed on a "stabilized" state,
- heads above the 'source' are now properly cleaned up,
# topics
Topics are an experiment to see if maybe the workflow defined by git
branches and hg bookmarks is only partially what users want - perhaps
something that feels more like a traditional VCS branch is right, but
that it should "dissolve" upon being finished. This extension exists
to be a sandbox for that experimentation.
# usage
Enable topics like any mercurial extension: download the source code to a
local directory, and add that directory to your `.hgrc`:
[extensions]
topics=path/to/hg-topics/hgext3rd/topic/