Trap recovery has been changed. The microcode attempts to determine

Trap recovery has been changed.  The microcode attempts to determine
how much state is valid and then saves all the pertinent information
(pc, registers, etc) so that the context of the trap and the rest of
the stack can be examined from scheme.

Primitives for reading/setting/enabling the keyboard interrupt
characters have been added.  There is now a single C keyboard
interrupt handler which dispatches according to the signal received
and what the current handler is supposed to do.

Scheme tty input has been rewritten for the NTH time.  reader_context
and reader_state structures have been merged.