Move the serialization lock from WT_CONNECTION into WT_BTREE, the btree
code is the only user.

If we're using pthread locking for spinlocks, lock initialization can
fail and we don't want to destroy uninitialized memory, track if the
lock was ever initialized.
Merge branch 'develop' into mutex-cleanup

Conflicts:
	src/support/global.c
Merge branch 'develop' into mutex-cleanup
Remove prototypes for __wt_cksum_hw/__wt_cksum_sw, they aren't needed
and they make lint unhappy when __wt_cksum_hw isn't referenced at all
(on non-x86_64 machines).
Cleanup the transaction state after a checkpoint.

refs #701
Fix a bug scanning through a memory-mapped file with overflow items (which is what LSM merges are doing all the time).

refs #701
Comment: explain why we copy the prefix before growing the buffer.
Merge pull request #704 from wiredtiger/mutex-cleanup

Mutex cleanup
Merge branch 'develop' into cache-dirty-bytes