Update "crosses branches"

[Rafael Villar Burke (Pachi)]

Dirkjan Ochtman wrote:
> The distinction between named and unnamed branches seems weird here,
> and it might well be a bug.
>
> FWIW, I agree that switching branches with a clean working dir should
> just work, but IIRC Matt was opposed to it.
IMHO, that makes sense, as allowing update to cross branches would make
an innocent "hg up" a potentially problematic operation if tip happens
to be in a different branch, as you'd be switching branches without
noticing and your next commits would end up in the wrong place.

Regards,

Rafael Villar Burke