added optional tlf_dir config option for storing .tlf files
fix test_sabotage tlf_dif
validate tlf_dir, exit with exitcode 45 on InvalidTlfDir
Merge remote-tracking branch 'refs/remotes/origin/ARAKOON-390' into 1.6

Conflicts:
	extension/server/ArakoonManagement.py
	src/node/catchup_test.ml
	src/node/collapser_test.ml
	src/node/node_main.ml
	src/system/startup.ml
	src/tlog/tlc2.ml
	src/tlog/tlc2_test.ml