Fix subtle idcache update bug in 'bk check'.
Fix subtle idcache update bug in 'bk check'.

When doing a check over a subset of files the code needs
to detect when the idcache is incorrect and rewrite the
cache if needed.  The code to notice problems could forget
that earlier files had problems when later ones were fine.

bk: 488103a36e66MwCiaFK-3eg0pTUCMA
bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper