Fixing the GameRegistry. Now it is possible to register a Block with a BlockItem using following code:
MyBlock myBlock = new MyBlock();
GameRegistry.registerBlock(myBlock, MyBlockItem.class, "myBlock");
where MyBlockItem class has one constructor with signature:
public MyBlockItem(int id, Block block)
Merge pull request #225 from MarcinSc/master

Suggested fix for issue 221