Add two new gradient columns, one where the start circle is has radius
0 and one where the end circle has radius 0. All the new gradients
except for one are rendered with a bright dot in the middle. In most
but not all cases this is incorrect.
Cc: ranma42@gmail.com
This test runs the new floating point combiners on random input with
divide-by-zero exceptions turned on.
With the floating point combiners the only thing we guarantee is that
divide-by-zero exceptions are not generated, so change
enable_fp_exceptions() to only enable those, and rename accordingly.
This separates the test suite from the random gtk+ using test
programs. "demos" is somewhat misleading because the programs there
are not particularly exciting (with the possible exception of
composite-test which shows off all the compositing operators).
