(kbd_buffer_frame_or_window): Restored old var.

(kbd_buffer_frame_or_window): Restored old var.
(kbd_buffer, kbd_fetch_ptr, kbd_store_ptr): Likewise.
(read_char_perdisplay): New var.
(read_char): Search all appropriate perdisplay objects, and do the right thing
if the next event comes from a different source.
(read_key_sequence): If there's a change of display in mid-stream, retreat and
try reading the new display.
(find_active_event_queue): Function deleted.  All callers changed to just test
the main kbd_buffer instead.
(kbd_buffer_store_event): Write to the main kbd_buffer again.
(kbd_buffer_get_event): Read from the main kbd_buffer again.
Now returns a perdisplay pointer in addition to a lispy event.
(Fdiscard_input, swallow_events): Use the main kbd_buffer again.
(stuff_buffered_input): Likewise.
(init_perdisplay): Initialize member kbd_queue.
Remove references to obsolete members.
(wipe_perdisplay): Remove obsolete reference.
(init_keyboard, syms_of_keyboard): Restore initialization of vars.