Add a new enchantement event on enchantItem

More information : https://github.com/MinecraftForge/FML/pull/446 and http://www.minecraftforge.net/forum/index.php/topic,18383.0.html
The only thing that is used in the following lines is the copy of the item stack. Simply renaming the two will decrease the patch size. Lines 77, 84, 85, 95, 104 and 109 (in the current patch, not the actual file) wouldn't be changed which would make it about half the current size.