dbug/dbug.c:
  function/ (a.k.a. SUBDIR) syntax
dbug/tests-t.pl:
  1. add support for test comments
  2. add test comments
  3. move tests around
  4. add SUBDIR tests
dbug/tests.c:
  support code for SUBDIR testing
include/my_dbug.h:
  comments. change in _db_set_ prototype
dbug/user.r:
  negative lists and function/ syntax.