Made dataBuffer be common for all holograms.
Reduced hologram memory usage by only pushing indexes of visible faces.
Clearing buffer when hologram isn't visible at all.
Removed debug println in hologram renderer (oops).
Fixed screen clicking via arrows a bit.
Caching shells for reduced memory consumption for nested os.executes.
Yet more OpenGL error checks.
Merge branch 'master' of github.com:MightyPirates/OpenComputers into MC1.7

Conflicts:
	src/main/scala/li/cil/oc/client/renderer/tileentity/HologramRenderer.scala
	src/main/scala/li/cil/oc/client/renderer/tileentity/ScreenRenderer.scala
	src/main/scala/li/cil/oc/common/block/Screen.scala
Formatting.