Log Message:
Fix a regression introduced between 0.29 and 0.30 detected when
handling large repositories like NetBSD src.  Problem found by riz@,
fix from mainline a:njs/d:2006-09-22T07:01:26, tested by me.

bump rev to nb1

ChangeLog:

2006-09-21  Nathaniel Smith  <njs@pobox.com>

        * lru_writeback_cache.hh (clean_insert): Correct the cache
        overflow logic so as to _actually_ never remove the last element.
        Add an invariant to verify this.
        (insert_dirty): Add an invariant here too.