Eviction of pages belonging to tables that have been force dropped.

There is currently a case in the MongoDB 3.0 family of releases, where using a debug build, a small cache and a series of rapid forced drop and create statements we can cause a diagnostic assertion to fire.

The case in question occurs when we fast track a page from a dropped table for eviction. The assertion in question checks if updates on the page are world visible, not taking into account the forced drop. After some review, the best action here on the 3.0 branches is to modify the assertion to include a check and not assert if the handle is marked DEAD