added various /SHOW0-ish statements to help when debugging internal

added various /SHOW0-ish statements to help when debugging internal
error handling

The MAKE-SPECIALIZABLE-ARRAY call in DEFUN INTERNAL-ERROR-ARGUMENTS
can become MAKE-ARRAY, since M-S-A is something to make it easier to
build parts of the cross-compiler under the cross-compilation host,
and DEFUN INTERNAL-ERROR-ARGUMENTS is in x86-vm.lisp, which is not
part of the cross-compiler, and so is never compiled by the
cross-compilation host.

changed MAKE-VALID-LISP-OBJ from a MACROLET macro to a global
function, for clarity and easier debugging

deleted unused SET-VALUE macro from MACROLET in DEFERR

deleted code marked REMOVEME, accidentally left over from previous
debugging exercises

changed CONTEXT-PC-ADDR, CONTEXT-PC, CONTEXT-REGISTER-ADDR, and
CONTEXT-REGISTER functions to use unsigned representations instead of
signed representations, to conform to implicit assumptions in the
debug-int code inherited from CMU CL. (Without this, new type errors
are generated in infinite regress when we try to handle errors
involving negative fixnums, e.g. (BUTLAST NIL -1).)

tweaked stuff in test/ directory a little bit in anticipation of
setting up real regression tests