Merge branch 'master' of https://github.com/daald/NBDServer into writefix

Conflicts:
	main.cpp

adding daald's (https://github.com/daald/NBDServer/) righteous changes to get write working despite 512byte
buffer issues
(cherry picked from commit 0d20ebf6b7eb6d13f0b1e5d9c22a8be2e5f07f72)