implementation of the decision to remove external frames

I made the needed changes in BLD, DTB, and FLD.

In the first two, I removed external frames and changed the appendix in DTB.

In FLD, I added two-argument External's so that  ATOMIC
externals could be supported (in other dialects). The 1-argument External was
restricted to match BLD, and it is now considered to be a shorthand for the
2-argument External. (BLD does not allow 2-arg externals.)

michael