Added references PDFs from TL12.

Renamed text-001.tex to formula-text-001 because text-001 is too
generic and test filenames should be unique across the tree.

This is because the files left in /diff and the produced table have
just the basename. Maybe it's worth a little refactoring to manage
them.

new file:   references/base/math/formula-001.pdf
renamed:    references/base/math-pln/math-pln-001.pdf -> references/base/math/formula-002.pdf
new file:   references/base/math/formula-text-001.pdf
renamed:    src/base/math/text-001.tex -> src/base/math/formula-text-001.tex
ignore the .pdf_original left by exiftool
Fixed the bottleneck of unique filenames

Now the filenames in different directories may be equal.

The diffs have now a prefix based on the path.
Promoted to references the PDF which have a minimal shifting

This is because they generated too much noise, but I left one just as
a reminder of the different distance between columns.

	modified:   references/base/core-des/core-des-002.pdf
	modified:   references/base/core-itm/core-itm-001.pdf
	modified:   references/base/footnotes/footnotes-001.pdf
	modified:   references/base/math/formula-001.pdf
	modified:   references/base/math/formula-text-001.pdf
	modified:   references/mkiv/spacing/spacing-grid-001.pdf
	modified:   references/mkiv/spacing/spacing-grid-005.pdf
	modified:   references/mkiv/structure/struc-allkind-xml-001.pdf
	modified:   references/unsorted/ppchtex-001.pdf
	modified:   references/unsorted/ppchtex-005.pdf
Dates will differ at each run, so left in a dedicated directory
	renamed:    references/unsorted/dates-001.pdf -> references/known-to-differ/dates-001.pdf
	renamed:    references/unsorted/dates-002.pdf -> references/known-to-differ/dates-002.pdf
	renamed:    src/unsorted/dates-001.tex -> src/known-to-differ/dates-001.tex
	renamed:    src/unsorted/dates-002.tex -> src/known-to-differ/dates-002.tex
remove useless ppm after the compare has been executed
*Huge* commit. Imported most of the official's tests from http://www.pragma-ade.com/download-1.htm

Only the PDF compiling took about an hour. I suppose a full test will
take 3-4 hours.
New option: --single <dir>

You can run a subset of the test using --single and targeting a single
directory (in references/ or src/).

This is needed because there are something like 900 testfiles now...
Promoted to references the PDF which have only distance shifting

	modified:   references/mkiv/backgrounds/textbackgrounds-001.pdf
	modified:   references/mkiv/bibtex/progressive-001.pdf
	modified:   references/mkiv/bibtex/traditional-003.pdf
	modified:   references/mkiv/bibtex/traditional-004.pdf
Added new test based on user's report.

The reference file has been generated by mkii

	new file:   references/contrib/math-integral-bug.pdf
	new file:   src/contrib/math-integral-bug.tex
Promoted to references two test with minimal shifting
	modified:   references/mkiv/bidi/alignments-002.pdf
	modified:   references/mkiv/bidi/floats-001.pdf
Improved visual diff output.

This slows down the tests, but makes the comparing easier, as it
leaves an annotated image in /diffs, not just a machine parsable file.
Broken in TL, promoted
	modified:   references/mkiv/blocks/blocks-001.pdf
Promoted. Minimal shifting and name: dummy -> name: koe
	modified:   references/mkiv/boxes/bleeding-001.pdf
	modified:   references/mkiv/boxes/collectors-001.pdf
	modified:   references/mkiv/boxes/offsets-001.pdf
Minimal shifting
	modified:   references/mkiv/catcodes/txt-001.pdf
Title distance shifting, promoted
	modified:   references/mkiv/chart/chart-003.pdf
Promoted chemical arrows (missing in TL). The axis file differs a lot.

	modified:   references/mkiv/chemical/alignment-001.pdf
	modified:   references/mkiv/chemical/arrows-001.pdf
	modified:   references/mkiv/chemical/ppchtex-001.pdf
	modified:   references/mkiv/chemical/ppchtex-002.pdf
output the warning about different page numbers to STDOUT
TL was missing the vertical bars
	modified:   references/mkiv/columns/columnsets-002.pdf
don't unlink the ppm if running under debug