Incorporate bde's code-review comments.

(a) bring back ttselect, now that we have xxxdevtotty() it isn't dangerous.
(b) remove all of the wrappers that have been replaced by ttselect
(c) fix formatting in syscons.c and definition in syscons.h
(d) add cxdevtotty

NOT DONE:
(e) make pcvt work... it was already broken...when someone fixes pcvt to
link properly, just rename get_pccons to xxxdevtotty and we're done