Ensure item stacks for GUI textures are always created with size 1
MC 1.8 client will render a red "0" over zero-size stacks
Added the "/stb validate" command
Also various tweaks in preparation for MC 1.8
Tested on highly unofficial protocol-hacked Spigot 1.7.10
  - if it breaks you get to keep the pieces
Merge branch 'master' of github.com:desht/sensibletoolbox