Extend scaling-crash-test in various ways

Extend scaling-crash-test in various ways

This extends scaling-crash-test to test some more things:

- All combinations of NEAREST/BILINEAR/CONVOLUTION filters and
  NORMAL/PAD/REFLECT repeat modes.

- Tests various scale factors very close to 1/7th such that the source
  area is very close to edge of the source image.

- The same things, only with scale factors very close to 1/32767th.

- Enables the commented-out tests for accessing memory outside the
  source buffer.

Also there is now a border around the source buffer which has a
different color than the source buffer itself so that if we sample
outside, it will show up.

Finally, the test now allows the destination buffer to not be changed
at all. This allows pixman to simply bail out in cases where the
transformation too strange.