subrepo: check phase of state in each subrepositories before committing

Before this patch, phase of newly created commit is determined by
"phases.new-commit" configuration regardless of phase of state in each
subrepositories.

For example, this may cause the "public" revision in the parent
repository referring the "secret" one in subrepository.

This patch checks phase of state in each subrepositories before
committing in the parent, and aborts or changes phase of newly created
commit if subrepositories have more restricted phase than the parent.

This patch uses "follow" as default value of "phases.checksubrepos"
configuration, because it can keep consistency between phases of the
parent and subrepositories without breaking existing tool chains.
largefiles: call super class method with proper kwargs to respect API

Since the localrepositoyry.push() method in mercurial/localrepo.py is defined
this way:

  def push(self, remote, force=False, revs=None, newbranch=False):

it is better for largefiles to call push() on the super class with proper
kwargs to respect the API.

This will avoid breaking other extensions overriding the push method this way:

  def push(self, remote, force=False, **kwargs):