(interrupt_signal) [MSDOS]: write explicit CRs since

(interrupt_signal) [MSDOS]: write explicit CRs since
stdout has been made binary.  Start at the top of the screen since
the internal terminal otherwise will write "below the screen."

[MSDOS]: #include <dos.h> and <time.h>, but not <sys/ioctl.h>.
(read_avail_input) [MSDOS]: Work around `ioctl'.  Also read through
dos_keyread for better keyboard support.
(interrupt_signal) [MSDOS]: Don't claim we can core dump.
(kbd_buffer_store_event): Cast a pointer to avoid a compiler warning.

(read_avail_input): Args to `kill' were backwards.
(kbd_buffer_get_event): If deleting last frame, call Fkill_emacs.

(modify_event_symbol): New arg NAME_ALIST.
Allow SYMBOL_TABLE to be an alist.
(Vvendor_key_alist): New variable.
(syms_of_keyboard): Initialize it.
(make_lispy_event): Handle vendor-specific keysyms.
(lispy_function_keys): Delete `remove' and th HP keysyms.

(read_avail_input): Turn O_NDELAY off on DGUX as on USG.