Adds a Check to prevent Biome Replacement

Splits the BiomeGenBase constructor to create one which takes a flag
that indicates whether to insert the biome object into the biomeList
array.  The standard constructor calls the new one with the default of
true.  This allows biome wrapper-objects to exist.
Merge pull request #841 from XCompWiz/biomecheck

Adds a Check to prevent Biome Replacement