[cairo] make-html.pl

[Baz]

To get my tests done this morning I fixed up a new bug in
test/make-html.pl - the addition of tests for 'similar' surfaces had
changed the log format, so what was printed out was junk. I think a
better fix is needed here though.

The script currently guesses the filenames of the test & ref images
and gets them wrong (eg if there is no rgb24 ref image, or if there is
a specific ref image for a backend). If we logged what was actually
compared and used that in the html it would be more robust. Would
anyone object to a change along these lines?

Old log format:
Testing scale-source-surface-paint with image target (dev offset 0)
Comparing result against reference image: ./scale-source-surface-paint-ref.png
TEST: scale-source-surface-paint TARGET: image FORMAT: argb32 OFFSET:
0 SIMILAR: 0 RESULT: PASS

Suggested log format:
Testing scale-source-surface-paint with image target (dev offset 0)
REF: ./scale-source-surface-paint-ref.png
OUT: ./scale-source-surface-paint-image-argb32-out.png
TEST: scale-source-surface-paint TARGET: image FORMAT: argb32 OFFSET:
0 SIMILAR: 0 RESULT: PASS

capitalizing the field names the script will parse. Tests that don't
have a REF will not produce an <img> tag in the output.

Cheers,
Baz