Accessing hidden commits by hash (directaccess extension)

[Danek Duvall]

This is great.  I've been hitting my head against this ever since I started
using evolve, and I'll be thrilled to have this functionality.

A couple of questions:

  - If a revision range is given that ends (or begins, I suppose) with a
    hidden changeset, will any intervening hidden changesets also be
    temporarily unhidden?

  - The recoverable-write commands often pop you into an editor before any
    warning can be seen and understood.  Should the warning be available in
    the editor template?

  - The unrecoverable-write commands could probably stand to explain why
    they're preventing the operation from happening, but perhaps more
    importantly, if you use --hidden with them, will they actually
    push/serve/whatever?  I guess I can see wanting a complete clone of a
    repo, including hidden changesets, so pushing them around would make
    sense in that context, but I thought we weren't going there.

Along similar lines, I've also wanted the ability to push and pull secret
changesets between (non-publishing) repositories, but only when specificied
by name like this.  Seems like there could be some shared mechanism there,
if it's not just me.

Danek