D421: hg: move part of top-level logic to dispatch.run

[quark (Jun Wu)]

quark added inline comments.

INLINE COMMENTS

> yuja wrote in hg:30
> This makes the import of `dispatch` non-lazy, right?

I thought demandimport was per module, non-recursive. It's obviously recursive. Will change.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D421

To: quark, #hg-reviewers, yuja
Cc: yuja, mercurial-devel