Mercurial's "phase" concept is important for evolution, and it's also
useful for filtering out uninteresting commits from log
output. Commits are typically marked "public" when they are pushed to
a remote. The CLI prevents public commits from being rewritten. Public
commits cannot be obsolete (even if they have a successor, they won't
be considered obsolete like non-public commits would).
This commits just makes space for tracking the public heads in the
View.
Git refs are important at least for understanding where the remote
branches are. This commit adds support for tracking them in the view
and makes `git::import_refs()` update them.
When merging views (either because of concurrent operations or when
undoing an earlier operation), there can be conflicts between git ref
changes. I ignored that for now and let the later operation win. That
will probably be good enough for a while. It's not hard to detect the
conflicts, but I haven't yet decided how to handle them. I'm leaning
towards representing the conflicting refs in the view just like how we
represent conflicting files in the tree.
I've forgotten to close a transaction a few times and while the
message ('assertion failed: self.closed') is clear to me now, it
probably won't be clear to others or to me in the future.
This extracts a bit from `Transaction::check_out()` for taking a
Conflict, materializing it, and writing the resulting plain file to
the store. It will soon be reused.
We currently recalculate the entire evolution state whenever a new
commit is added within a transaction. That's clearly wasteful. This
commit makes the state-update incremental.
