[PATCH V2] amend: new extension providing the amend command

[Jun Wu]

Excerpts from Gregory Szorc's message of 2017-07-13 08:03:42 -0700:
> I'm late to the review party.
> 
> When I saw this patch, I thought an extension was a bit heavyweight. I was
> wondering if we could achieve something similar by defining a [commands]
> option or 2 for changing behavior of prompting for commit message during
> --amend. Then you would just need to [alias] your way to victory.

I have thought about it. [commands] is what we want eventually. But
[commands] support is not as mature as [extensions] today. For example, if a
user types "hg amend", hg prompts them to enable the extension. Once we can
make [commands] version as discoverable as extension, amend could be moved
to core.

> That being said, there is value to squatting on "amend" in core: it is a
> useful name. So I have nothing against this patch. I'm just trying to
> encourage use of [commands] for doing useful things.