FIX: [mysql] too long index keys leads to 1071 on innoDb (fixes #14117) + missing music db indexes after recent db bump

/cc @jmarshallnz 

Refers to http://trac.xbmc.org/ticket/14117

As this not really prio 1, I suggest to only merge this at the last minute (before RC or BETA ?) to prevent unnecessary bumping if other mysql issues are discovered.