hghave: add some official category for known-bad and missing-good output
This will make it simple to tag output that are expected to changes. A simple
hghave integration seems enough but smarter behavior around these seems possible
in the future.
Differential Revision: https://phab.mercurial-scm.org/D9607
Test issue2761
$ hg init
$ touch to-be-deleted
$ hg add
adding to-be-deleted
$ hg ci -m first
$ echo a > to-be-deleted
$ hg ci -m second
$ rm to-be-deleted
$ hg diff -r 0
Same issue, different code path
$ hg up -C
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ touch does-not-exist-in-1
$ hg add
adding does-not-exist-in-1
$ hg ci -m third
$ rm does-not-exist-in-1
$ hg diff -r 1