*: lock the in using files; do not purge locked the wal files
*: do not backup files still in use
wal: rename openAtIndex -> open; OpenAtIndexUntilUsing -> openNotInUse
test: add fileutil to test
wal: fix wal doc
Merge pull request #1927 from xiang90/flock

*: lock the in using files; do not purge locked the wal files