Instead of tagging the sources, which is insensitive to changes, track the
known failure modes by recording the current fail as an xfail.png
reference. (We also introduce a new.png to track a fresh error, so that
they are not lost in the noise of the old XFAILs and hopefully do not
cause everyone to fret).
As we have removed the XFAIL tagging we find, surprise surprise, that some
tests are now working -- so review all the reference images (as also some
.ref.png now should be .xfail.png).
Note: I've only checked image,pdf,ps,svg. The test surfaces report some
failures that probably need to addressed in source. I've not correct the
changes for win32 and quartz. Nor fixed up the experimental backends.
extend-pad was not a clear demonstration of the EXTEND_PAD mode, so revamp
it to show the filter extending a 4 pixel surface to cover the entire
output. However, this hides a discrepancy with the vector surfaces that we
cannot prevent the external renders from applying an interpolation to the
border pixels, so we copy the original test to extend-pad-border to check
the desired behaviour on boundary pixels.
