Qhull for 3.6.0

[John W. Eaton]

On 12-Dec-2011, Rik wrote:

| Qhull
| Modify configure.ac to detect versions < 2010 and versions > 2010
| #ifdef in Qhull code to include the correctly named library

I don't think we want to check version numbers.  I checked in the
following change:

http://hg.savannah.gnu.org/hgweb/octave/rev/f913363318e0

Depending on how qhull is compiled, it may be necessary to define
qh_QHpointer=1 before including qhull.h.  I'd like to have a configure
test for that, but I don't know how to write it.  Either that, or I'd
like to have a way to avoid having to define a macro like that at all,
since it seems like an implementation detail of qhull that we should
not have to know about just to use qhull.

jwe