WOFF: Compress & write the font tables in the same order as the origi…

[fred-wang]

…nal sfnt font so that the checkSumAdjustment does not change when the font is decompressed again. Also add a Python test to verify that the WOFF files generated by fontforge are valid. #926

[fred-wang]

The relevant quotation from http://www.w3.org/TR/WOFF/:

Font tables in WOFF files MUST be stored in the same order as the well-formed input font. The table order is implied by offset values in the table directory; sorting table directory entries into ascending offset value order produces a list of entries in an order equivalent to that of the font tables.

[frank-trampe]

It looks good.

[fred-wang]

Thanks! I guess #926 can also be closed, unless there are reasons why checkSumAdjustment can be invalid other than wrong table ordering.

[jtanx]

So, after looking at #2762, I've found that the added test doesn't work on Python 3 - which all FF unit tests should conform to. Travis wasn't picking this up, because test926.py wasn't added to EXTRA_DIST in Makefile.am so the test was being skipped.