nesting of EVAL-WHENs

[Jon L White <edsel!jonl@labrea.stanford.edu>]

I'm going to need some more time to think about this question, but vaguely
I thought the model of eval-when processing tried to make sure that subforms
only got evaluated once when there were multiple applicable situations.
For the interior eval-when(eval compile load), the first evaluation during 
compilation is because of the EVAL situation in the outter eval-when; then
the second "potential" evaluation is during the compilation of the inner
eval-when, when it notices that it has the 'compile' situaiton.  Clearly
we need to insure that the eval-when model has a state that says:
   "compiling, but have already eval'd this"

-- JonL --