[PATCH 0 of 3] hbisect: tolerate unusual but consistent bisect situations

[Alexander Krauss]

In certain situations (when the earliest good revision is not an
ancestor of the earliest bad one), bisect incorrectly claimed
"inconsistent state". Apparently, it was assumed that such situations
cannot occur, which is only true if the user strictly follows the
bisect sequence suggested by Mercurial. Adding other information to
the bisect state via "hg bisect -g REV" easily produces such a
situation.

Patch 3 in this series adresses the issue and adds a test. The rest
are minor clarifications.

Alex