curses EDIT_GETLIN - discarding preloaded answer

curses EDIT_GETLIN - discarding preloaded answer

EDIT_GETLIN is more complicated on curses than on tty due to way that
long lines are handled....

Using ESC to get rid of the default response removed it from the
answer buffer but didn't erase back to the end of actual prompt,
making it look as if it was still there.  Fixing that for a one-line
prompt+answer was needed and would have been easy but it also needs to
be prepared to go back to prior lines.  Both the prompt and the answer
could conceivably span lines although in practice it will usually just
be one line or else prompt+answer combined spanning to a second line.

This hasn't been exhaustively tested been seems to be working correctly.