subrepo: use hg.repository instead of creating localrepo directly
this way, extensions' reposetup will be called, which allows for git
subrepos to be handled by hg-git (and I believe the same goes for
svn and hgsubversion)
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
removing b
created new head
% should abort
abort: crosses branches (use 'hg merge' or 'hg update -C' to discard changes)
% should succeed
abort: crosses branches (use 'hg merge' or 'hg update -C')