Renamed capacitor upgrade to battery upgrade and introduced two additional tiers. Closes #280.
Generalized rarity computation for items (less code per item, yay).
More OpenGL error checking all over the place.
Merge branch 'master' of github.com:MightyPirates/OpenComputers into MC1.7

Conflicts:
	src/main/scala/li/cil/oc/Items.scala
	src/main/scala/li/cil/oc/client/renderer/WirelessNetworkDebugRenderer.scala
	src/main/scala/li/cil/oc/common/item/Delegate.scala
	src/main/scala/li/cil/oc/common/item/GraphicsCard.scala
	src/main/scala/li/cil/oc/common/item/InternetCard.scala
	src/main/scala/li/cil/oc/common/item/LinkedCard.scala
	src/main/scala/li/cil/oc/common/item/Microchip.scala
	src/main/scala/li/cil/oc/common/item/NetworkCard.scala
	src/main/scala/li/cil/oc/common/item/RedstoneCard.scala
	src/main/scala/li/cil/oc/common/item/UpgradeAngel.scala
	src/main/scala/li/cil/oc/common/item/UpgradeCrafting.scala
	src/main/scala/li/cil/oc/common/item/UpgradeExperience.scala
	src/main/scala/li/cil/oc/common/item/UpgradeGenerator.scala
	src/main/scala/li/cil/oc/common/item/UpgradeInventory.scala
	src/main/scala/li/cil/oc/common/item/UpgradeNavigation.scala
	src/main/scala/li/cil/oc/common/item/UpgradeSign.scala
	src/main/scala/li/cil/oc/common/item/UpgradeSolarGenerator.scala
	src/main/scala/li/cil/oc/common/item/WirelessNetworkCard.scala