* app/composite/gimp-composite-dispatch.[ch]: regenerated new code
taking advantage of simplified function prototypes.

* app/composite/gimp-composite-test.c: New regression testing
driver.  This file is automatically generated, but it's included
in the cvs tree for expediency.

* app/composite/ns.py: hopeful checks for which OS is currently
running as a hint to what nm(1) is available.

* app/composite/gimp-composite-mmx.[ch]
* app/composite/gimp-composite-sse.[ch]
* app/composite/gimp-composite-generic.[ch]: function prototype
cleanup.

* app/composite/make-gimp-composite-dispatch.py: generates code to
test compositing functions.

* app/composite/gimp-composite-regression.[ch]: support for
automatically testing compositing functions.