Fix previous commit(s)

- Make FILES and SCRIPTS a dependency for all so they're built as
  part of the "many" case.
- Deal with PROGS being empty and SCRIPTS not being empty (this was the
  case that jmmv was originally trying to fix). This can be reproduced
  by going to tests/sys/pjdfstest, and just installing that directory
  (the previous commit wouldn't install kyua.sh and misc.sh).

Sponsored-by: EMC / Isilon Storage Division