refactor FOP table and stack handling

refactor FOP table and stack handling

 Just two special variables *FOP-TABLE* and *FOP-STACK*.

 Both hold a simple-vector, whose first index holds the index of the last
 element. These are always freshly allocated -- no more *FREE-FOP-TABLES*
 dirtying up the old generations.

 Define a semi-opaque interface for manipulating the stack and the
 table. (Mainly replacing explicit SVREF's with REF-FOP-TABLE.)

 ...and lo! Our fasl-loading speed sucks 5-10% less.