Resolve double build number issue

Signed-off-by: Steven Downer <grinch@outlook.com>
Improved Server Version Check

This ensures that if the server is not running the supported CraftBukkit
version (Currently 1.6.4-R2.0 and 1.6.4-R2.1) that it will not continue
loading and instead SpoutcraftPlugin will disable itself and give a
warning in the console.

Screenshot of warning: http://i.imgur.com/Ha1JqF7.png

Signed-off-by: Steven Downer <grinch@outlook.com>