Return bukkit compatibile recipe when calling toBukkitRecipe(). Fixes #176, #284

In previous builds, plugins that tried converting any IRecipe to a bukkit
compatible Shaped/ShapelessRecipe would instead receive a CustomModRecipe
which Bukkit knows nothing about. To workaround this issue, I now hold a
reference to each vanilla recipe passed into Forge in order to return a
bukkit compatible recipe.