(REGISTER_U_ADDR): Fix up for Ultrix 4.2.
* tm-tahoe.h, xm-tahoe.h (KERNEL_U_ADDR): Move macro to xm-tahoe.h.
* stack.c (_initialize_stack): "dow" should be a valid abbreviation
for "down". Suggested by Richard Stallman.
basis. See comments in objfiles.h and details in ChangeLog. Also remove
redundant definitions of FRAME_CHAIN_VALID from most of the tm-* files and
use a default definition in frame.h.
READ_MIPS_FORMAT, which have been unused since BFD. Still
remaining is COFF_NO_LONG_FILE_NAMES.
* tm-sun3.h, tm-altos.h: Remove detritus accidentally left from
function calling code moved to m68k-tdep.c.
