EMI: Load both music-tables, and require both. (RFC)

This adds loading of both FullMonkeyMap.imt's as the convention we have on the wiki is:
FullMonkeyMap.imt (cd1)
FullMonkeyMap2.imt (cd2)

This requires user-intervention, in the form of copying the second file from CD2, and renaming it.

In addition, perhaps we should check that certain entries exist after loading, to verify that the user hasn't overwritten one of the files wrongly (although, putting them in the wrong order is no problem).

And, perhaps add MD5-checks for both files?

This also makes the files REQUIRED for the game to start, this can of course be changed into "Do you want to continue without music", but atleast it makes it clear to the user what's wrong.

Comments, and simplification on the error-message, is very welcome.