[cairo] dash phase oddity

[Baz]

I am looking at the remaining dash tests that fail on quartz
(dash-state, degenerate-path), which all seemed to be similar -
degenerate dashes, which appear as circles or squares in the cairo
tests, aren't being drawn because quartz isn't hitting dash-on at the
same phase as cairo. So I did the obvious thing an added a random tiny
amount to the phase:

-       CGContextSetLineDash (surface->cgContext, style->dash_offset,
fdash, max_dashes);
+      CGContextSetLineDash (surface->cgContext, style->dash_offset +
0.00001, fdash, max_dashes);

... and hey presto, all of these tests look good (but still fail due
to tiny differences in antialiasing and because quartz won't draw a
line cap and a mitre join at the same point)

So... do we care enough to want a fix along these lines, or should I
just forget it and add a ref image? (I'm guessing the latter, just
curious)

-Baz