subres --> spmod



For the next release, I suggest that we consider making spmod the default 
gcd algorithm.
So that everybody can try this out, this morning I committed this change. 
The test suite
seems to run OK (sbcl 1.0 for windows)

Building Maxima under windows is getting more difficult:

(1) I think configure  requires perl version 5.8, but mingw only has 
version 5.6

(2) My GCL 2.6.7 builds a Maxima that seems to work, but the
test suite reports lots of error breaks (I think this is a problem with
line endings)

(3)  I haven't found a place to download GCL 2.6.8 binaries for windows.
I haven't tried to build it for myself.

Fortunately, many changes can be tested without re-building.

Barton