[RIF] Test document

I made some fairly minor updates to the test document to include Core
and PRD.  The document needs more work (particularly test metadata,
and updating section 6 to give guidance on creating runnable test
cases), but the current changes plus a few since the last working
draft (new ImportRejection test type) might warrant publishing a new
draft, I'm not sure. The semantic tests section [1] should definitely
be checked to see if it's appropriate for PRD. PRD doesn't define
entailment, and I defined the test in terms of condition satisfaction.
Also, not sure if the current definitions adequately address testing
an execute action such as print.

Stella

[1] http://www.w3.org/2005/rules/wiki/Test#Semantic_Tests