Got rid of the MagicWord indexing constants (MAG_xxx), replaced them by string indexi...

Got rid of the MagicWord indexing constants (MAG_xxx), replaced them by string indexing, like messages. The associated change to the extensions, i.e. removing the MagicWordMagicWords hook and using string instead of integer indices, is in fact compatible with MW 1.6 and 1.7, which tells you something about the utility of the hook function.