Recent "apitrace trim" is now dropping uninteresting calls by
default. This means that the call numbers of rendering operations are
changing. Consequently, image comparisons were failing not due to
image-content differences, but simply because the filenames (with
embedded call numbers in them) no longer matched.
We can avoid this problem by using the --call-nos=no option which was
added to "apitrace dump-images" in very recent versions.