ARAKOON-418 fsync=true should be the default, warning otherwise
disable fsync by default for most tests
more fsync disabled in tests; test progress possible with fsync enabled
don't fsync tlog during catchup

Conflicts:
	src/node/catchup.ml
fix test_fsync
fix test_learner by disabling fsync (makes the timing assumption true again)
Merge pull request #209 from Incubaid/ARAKOON-418

ARAKOON-418 fsync=true should be the default, warning otherwise