Add more precise checking for results not used for functions like
NREVERSE and DELETE. When given vectors, the vectors are modified
in-place, so we don't have to use the result.
compiler/fndb.lisp:
o Functions like NREVERSE and DELETE that take sequences need to check
to see if the sequence might be a list or not before warning about
if the result is not used.
o MERGE needs a fancier :result-not-used function, so disable that for
now.
compiler/knownfun.lisp:
o LIST-FUNCTION-RESULT-NOT-USED creates a function to check is the
specified arg is a list and determines if the result is used or not.
