Addition of SkipListCache#locatePage(K, LockMode, boolean) method
that allows for fetching a page with the exact key value, instead of
the default floor key value. This feature is used by the skiplist
iterator to ensure that the iterator will not enter an infinite
loop in the presence of invalid nextFirstkey values. In pageDB
testing and repair adding check to ensure that all keys on a page
are less than the firstKey on the next page.