[PATCH] dirstate: make subrepos an optional arg to status() and walk()

[Greg Ward]

Oops, I forgot to flag this one "stable".  It's my last-ditch attempt
to make dirstate.status() and walk() compatible with existing
extensions that work with the 1.4 API.  If this does patch not go into
1.5, then it's pointless.  I'll just have to suck it up and find a way
to fix my extensions that call and/or wrap dirstate.status().

(Incidentally, there is a pending change to bfiles whose cleanest
implementation involves another change to the dirstate.status() API.
So there might be another change coming to this code post-1.5, and I
think making these changes with optional keyword args will make life
easier for extension authors in general.  I.e. my current patch feels
like a move in the right direction for future changes to build on.
Just my opinion, of course.)

Greg