revert this change from early this year.  it appears the
changes macallan@ commited to fix FIRMWORKSBUGS issues
in openfirmware() have fixed the hangs seen on PegasosII.

hooray!

---
Log Message:
workaround a problem with the pegasos firmware interface:
attempting to use /dev/openfirm on this machine hangs hard.

this isn't a new problem, and i've been meaning to try to
figure it out for years, but it's become a problem since
the xf86-video-radeon driver gained code to look for the
macppc model using this interface.

this is why xorg-server 1.18 and 1.20 hang recently on the
pegasosII.

this change is fairly ugly but i couldn't think of a less
ugly method to avoid /dev/openfirm working just on this
one platform.  introduce new __OPENFIRMIO_OPEN_CHECK_BROKEN
macro and associated __openfirmio_open_check_broken(), and
use them in the new openfirmopen() to fail opens.

include proplib.h in macppc and ofppc autoconf.h since they
use it.
---

(mrg)