rename FPBASE to _FPBASE, so that we avoid polluting the user's
name space when e.g. <sys/ptrace.h> is included. Previously, the
PC symbol in mips/regnum.h would conflict with the declaration of
the external variable by the same name in termcap.h, as discovered
by the ``okheaders'' regression test.
* define PT_GETREGS and PT_SETREGS in pmax/include/ptrace.h
* Flesh out the stubs in pmax/pmax/process_machdep.c to handle
those requests.
* Now that "struct reg" is actually used, remove the bogus
#ifdef LANGUAGE_C around its definition, and redo pmax/include/reg.h
so that the definitions needed by locore.S are in a separate file,
pmax/include/regnum.h.
* update locore.S to match.
