repo: move visibleheads and visiblebranchmap logic in discovery...
repo: move visibleheads and visiblebranchmap logic in discovery
They were previously inside the mercurial.phases module, but obsolete
logic will need them to exclude `extinct` changesets from pull and
push.
The proper and planned way to implement such filtering is still to apply a
changelog level filtering. But we are far to late in the cycle to implement and
push such a critical piece of code (changelog filtering). With Matt Mackall
approval I'm extending this quick and dirty mechanism for obsolete purpose.
Changelog level filtering should come during the next release cycle.
