Keep track of family instance modules

- Now each modules carries
  (1) a flag saying whether it contains family instance declarations and
  (2) a list of all modules further down in the import tree that contain
      family instance declarations.
  (The information is split into these two parts for the exact same reasons why
  the info about orphan modules is split, too.)
- This is the first step to *optimised* overlap checking of family instances
  coming from imported modules.

*** WARNING: This patch changes the interface file format! ***
***          Recompile libraries and stage2 from scratch!  ***