tests/test-default-push.t

convert: add config option for disabling ancestor parent checks

When converting merge commits, convert checks if any of the parents are
ancestors of any of the other parents. To do this, it builds an ancestor list
for every commit in the repository. On large repos this can take a long time
(30min+). Let's add an option for disabling this check to preserve performance.

The downside of this is that it may create unnecessary parent connections when
enabled (which is unfortunate, but not incorrect).

To verify, I ran the convert tests with the flag enabled, and verified the graph
changes were all just to add new parents that were ancestors of existing
parents.

  $ hg init a

  $ echo a > a/a
  $ hg --cwd a ci -Ama
  adding a

  $ hg clone a c
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg clone a b
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ echo b >> b/a
  $ hg --cwd b ci -mb

Push should provide a hint when both 'default' and 'default-push' not set:
  $ cd c
  $ hg push --config paths.default=
  pushing to default-push
  abort: default repository not configured!
  (see the "path" section in "hg help config")
  [255]

  $ cd ..

Push should push to 'default' when 'default-push' not set:

  $ hg --cwd b push
  pushing to $TESTTMP/a (glob)
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files

Push should push to 'default-push' when set:

  $ echo '[paths]' >> b/.hg/hgrc
  $ echo 'default-push = ../c' >> b/.hg/hgrc
  $ hg --cwd b push
  pushing to $TESTTMP/c (glob)
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files