Fix a bug in recovery with missing files (e.g., after a hotbackup that raced with file creation).

refs #1042
Fix some LSM latency issues:
* have merge threads periodically check whether the tree needs to be switched in case the checkpoint thread is blocked; and
* don't turn on os_cache_dirty_max by default for LSM.
Merge pull request #1051 from wiredtiger/lsm-latencies

Fix some LSM latency issues
Merge pull request #1045 from wiredtiger/recover-missing-files

Fix a bug in recovery with missing files
Change test1-4 to max out with 2 billion items.
Add custom key sorting function for times. #1052