This will be needed to fix bug 386 (WLUR).
Added new prfs idx_modarray_AxSxS and idx_modarray_AxSxA to
reflect changes in modarray and to have a clear separation between
scalar valued and array valued modarrays in the code generation.
Stripped dead prf switches out of compile, makedimexpr and makeshapeexr
after they have been replaced by proper function tables.