Made this actually work when there's an object directory:

Made this actually work when there's an object directory:
- replaced bogus dependencies of distribution sources on generated
  sources by the same ones that bsd.lib.mk would generate if it knew
  all the sources.  We shoot ourself in the foot by not naming the
  generated (included) sources *.h, so we can just put the generated
  sources in SRCS.
- replaced -I${.CURDIR} by `-I.'.  Here `.' is an alias for ${.OBJDIR}.
  -I${.CURDIR} didn't do anything, since ${.CURDIR} is the default in
  all cases here (it would be necessary for ""-style includes made from
  sources in ${.OBJDIR}.

Don't use `+=' for setting CLEANFILES for the first time.

Added $Id$.