[CHANGESET]: First attempt at a single precision type.

[David Bateman]

Its not attached to this message as the changeset is nearly 5MB in size,
but I have a working and reasonably complete adaptation of Octave to
allow the use of single precision types. It can be found in my mercurial
repository at

http://hg.dbateman.org/octave

and it is changeset number 8002 (1e224fa7f5bc).

Basically, as this is just a copy of the double precision type I'd
always thought it would be relatively easy to add this. With that idea I
didn't attempt to make template versions of the copied code to reuse it
and just copied it as the easier fashion to get this working. Therefore,
there might be some simplifications that might be done..

Also although I've converted most functions to allow floating point
types (or rather those that made sense to be modified), I haven't
converted some including some basic ones like find and quad.

I've assumed that the correct mixed double/single behavior is to promote
the single type to double, and so I've used the numeric conversion
function of the octave_value to do this rather than have to define all
of the mixed type opeators.

Finally it has had little testing, and in fact doesn't have any test
code for it at all yet. I suppose that almost all of the existing test
code  should be converted to allow floating versions. I'm sure there is
some easy way to do that but I'm not sure I see it. However, I'd rather
get the code out there before going further, to allow feedback on the
patch and for others to test the code out and if motivated to contribute.

Regards
David