Overhaul of Java auto-detection

[Rik]

12/10/12

All,

I just pushed a changeset which significantly changes (improves?) the way
Java is detected if JAVA_HOME has not been set
(http://hg.savannah.gnu.org/hgweb/octave/rev/56239ff815a3).  There are
likely to be kinks which need working out and I particularly need feedback
from Mac OS X systems.  Despite all those caveats, I think this is a much
better strategy for detection than having a laundry list of directories to
check for each operating system and distribution.

--Rik