Move forced eviction into application threads.  This is a major cleanup of the eviction server, and application threads are going to be blocked from accessing the page regardless, so there is no disadvantage.
Merge branch 'develop' into app-forced-eviction

Conflicts:
	src/include/wiredtiger.in
Merge pull request #505 from wiredtiger/app-forced-eviction

Move forced eviction into application threads