Readme:
-Recommend openjdk 7 for Debian/Ubuntu
-It is tested on Debian.
-Rm bukkit section now that bukkit is dead.
Remove code to download bukkit and sportbukkit jars, since those websites are unlikely to come back up.
Switch from usign screen to using tmux, because screen seems to be
buggy and sometimes fails at startup. In particular, screen seems to
always fail on first run after installation on a fresh Debian 7.
Merge remote-tracking branch 'upstream/master'