expose HTable#setAutoFlush through the --buffer-writes option

I'm pretty sure this is extremely unsafe, and doesn't care about ordering, so
it should only be used with insert-only tailers.
we don't need to delete the individual tables, since the whole cluster disappears
add a test for an insert-only tailer with bufferWrites set to true
bump waiting threshold in tailer test
kill tailer thread in tests in a better way
fix a really stupid bug where timestamps weren't being saved every 60 seconds
set optime correctly when picking up where we left off
bump version to 0.3.2