require Poppler 0.76.0 for ignoreDiacritics feature
instead of 0.73.0 (where it was first implemented) because 0.76.0 includes a fix for a regression that caused non-ascii search terms (like in eg. Russian) to not match anything when using the ignoreDiacritics option.
The workaround is to use the 'case sensitive' search option (because using 'case sensitive' automatically disables ignoreDiacritics inside Poppler).
But given that Fedora 30 (and probably other distros) ship Poppler 0.73.0, we better require the regression fixed version of Poppler, so to not regress on users which search text in the affected languages.
Issue #1179 (closed)
Closes #1179 (closed)