Changes to tune eviction loops based on profiling.  Track more pages, but only sort the maximum number of entries we have actually seen.
Merge branch 'develop' into eviction-tuning

Conflicts:
	src/btree/bt_evict.c
Merge branch 'develop' into eviction-tuning

Conflicts:
	src/btree/bt_evict.c
Merge pull request #508 from wiredtiger/eviction-tuning

Changes to tune eviction loops based on profiling.