ExtendedBiomeDictionary?

I was requested to submit a PR, so I did.

In essence, I believe that with 1.7.2 a new biome dictionary is needed in order to accommodate the new biomes.  Savannah and Mesa pretty much need their own categories.  Taigas, due to their diversity also got their own category.

There's a several new definitions I added mainly for biome adding mods, give or take.  

I also made a attempt at making the register try to find biomes in the new categories I added, but I doubt it works.  For instance I wanted to define mesa biomes by checking if the biome is hot and generates hardened clay, but being new to coding I just left a comment with the block ID.  

Original thread [ignore the different definitions]:

http://www.minecraftforge.net/forum/index.php/topic,19610.0.html