Add a machinetype identifier to help us quickly identify
Apple //e (bit 7) and //e enhanced (bit 6).
Use it in conio functions for 80-columns code instead of
relying entirely on the __APPLE2ENH__ target.
Move videomode() to the apple2 target, and have it return
an error if 80-columns hardware is not available - this
is a lie for now, it is considered available on //e enhanced,
which may not be true, and not available on //e, which
may also be not true. An ulterior patch will make that
check correctly.
Adapt the box/line drawing characters so that one can use
MouseText on the apple2 target if it is available, by
defining DYN_DRAW_BOX. No change by default: MouseText is
considered available on apple2enh and not available on
apple2.
