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
Merge pull request #704 from wiredtiger/mutex-cleanup

Mutex cleanup