discovery: move code to create outgoing from roots and heads changegroup.changegroupsubset() contained somewhat low-level code for constructing an "outgoing" instance from a list of roots and heads nodes. It feels like discovery.py is a more appropriate location for this code. This code can definitely be optimized, as outgoing.missing will recompute the set of changesets we've already discovered from cl.between(). But code shouldn't be refactored during a move, so I've simply inserted a TODO calling attention to that.

  $ rm -rf a
  $ hg init a
  $ cd a
  $ echo a > a
  $ hg ci -Am0
  adding a
  $ hg tag t1 # 1
  $ hg tag --remove t1 # 2

  $ hg co 1
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg tag -f -r0 t1
  $ hg tags
  tip                                3:a49829c4fc11
  t1                                 0:f7b1eb17ad24

  $ cd ..