Increase the likelihood of being able to evict hot pages.

Specifically pages that grow larger than the configured maximum.
Also, don't attempt eviction unless it's possible that we'll succeed.
Add macro to check for a transaction with updates and Lint.
Merge pull request #604 from wiredtiger/force-evict-tuning

Increase the likelihood of being able to evict hot pages.
Merge branch 'develop' into fine-grained-durability.

Conflicts:
	src/include/txn.h