Log message:
Import eag, provided by Jaap Boender in PR pkg/22795 and modified by me.

Extended Affix Grammars (EAG) are an attempt to implement a very
general form of Affix Grammars, with very few restrictions.  EAG can
be used as a specification formalism, specifying in general relations
rather than functions, or as a relational programming language similar
in many respects to PROLOG.