Per branch ignore exclusions

[John Whitley]

Martin Pool <mbp <at> canonical.com> writes:
> Since we support Python regexps in ignore rules, it may already be
> possible to use a negative-match regexp to do this.  If there is, it
> should be documented as as recipe; if not it would be worth filing or
> duping a bug.

I didn't see a dupe, so I filed as:
https://bugs.launchpad.net/bugs/428031

Good idea, re: regexps.  Depending on the ignore implementation, a
negative-match regexp may or may not work as the user expects.  It
might require collapsing some or all ignore rules into a big ugly
alternate-list regexp.  If the ignore engine already compiles the
rules into a big regexp, a negative matcher might be ok.

In any event, I plan on starting by hacking out some (failing)
exclusion tests and will use that time to see if a negative-match
regexp approach will indeed work.

-- John