Rather than only calling "Init" on a "SIMPLE" module type, just
check that it is not invalid instead.  Even extension types
still have an Init routine that needs to be called.

Implements a differently-named function instead, which does mostly the same thing,
but does not directly re-add the original subdirectory.  This does repeat some
info (e.g. the list of FSW source files) that was not repeated otherwise, but
it works in general.

Fix #303, check that module type is not invalid

Fix #305, do not override add_psp_module for coverage test

Part of nasa/cFS#351