TST : force re-building of font-cache

 - there should be a better way to do this, this will get the
   tests passing again.
Fix cyrillic characters coming from LaTeX, saving in PDF
Merge pull request #3074 from tacaswell/fp_fix

TST : force re-building of font-cache
Merge pull request #3076 from mdboom/russian

Bug: backend_pdf: UnicodeDecodeError: 'ascii' codec can't decode byte 0xe2