added --worldsize

You can now define the size of the world by --worldsize [number].
suggest even numbers only.  kytten is for potential future reference.
Merge branch 'master' of git://github.com/BertrandBordage/Minecraft
Merge branch 'master' of git://github.com/ronmurphy/Minecraft
Bugfix
Fix to earlier "fix".
Moved ItemSelector to gui
Removed extra GLOBALS
Items dir should be a directory
Merge https://github.com/boskee/Minecraft

Conflicts:
	blocks.py
Destroys leaves + fix.