XSB Src (SVN)-old

Updating a number of files so that delete_branch() will work with call
subsumption (it needs to know that it deallocates BTNs rather than
TSTNs). This fixed a latent bug in simplification and allows another
test to be run for call subsumption. It also provides a step towards
supporting answer subsumption on call subsumptive tables. There are
also some other documentationstyle changes.

Adding a new test for copying attributed variables into delay elements
/ lists. I hadn't thought this worked, but apparently it does !

Also, I'm adding a very simple test for incremental evaluation -- more
cases need to be added here, but at least this is a start.