REDUCE Code

Revise getd to return a function pointer for a compiled function
instead of always returning a lambda expression. Generalise explode
to handle function pointers. Revise yesp to output its message with
better spacing and lower-case identifiers. Enable the SBCL
interactive debugger only if the input and output are both
interactive. Enable initial compilation on SBCL only if *comp is
true. Remove eval-when from the definition of eqcar. Revise some
comments.