As part of separating dirstate business logic from storage, let's move the
nonnormal and otherparent storage to the dirstatemap class. This will allow
alternative dirstate storage to persist these sets instead of recomputing them.
Differential Revision: https://phab.mercurial-scm.org/D979
This adds a test extension to check that the non-normal set contains the
expected entries. It wraps several methods of the dirstate to check that
the non-normal set has the correct values before and after the call. The
extension lives in contrib so that paranoid developers can easily
enable it to make sure that the non-normal set is consistent across more
complex operations than the included tests.
