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.
If there's an entry in the cache with the same key as the entry in the
primary, but the cache has been deleted, ignore both and move to the
next entry.

Remove the code that handled the case where the CURSOR key referenced
memory in the WT_CURSOR: that can no longer happen because of the change
to always copy the memory from the WT_CURSOR.
Merge pull request #604 from wiredtiger/force-evict-tuning

Increase the likelihood of being able to evict hot pages.
style: u_int32_t -> uint32_t, TXN_FORCE_EVICT no longer used.
Overwrite pages when they're free'd, in diagnostic mode, hopefully that
will help catch subsequent use of evicted pages.
Merge branch 'develop' into memrata

Conflicts:
	src/include/txn.h