XeTeX: accept PDF version 1.7 without warnings
At least for my combination of XeTeX (TexLive 2017, 3.14159265-2.6-0.99998) and GS (9.26), xdvipdfmx outputs a bunch of error messages during PDF compiling:
xdvipdfmx:warning: Version of PDF file (1.7) is newer than version limit specification.
xdvipdfmx:warning: pdf_open: Not a PDF 1.[1-5] file.
xdvipdfmx:warning: Trying to include PDF file which has newer version number than output PDF: 1.5.
This clutters up the logs and makes it harder to spot potential errors.
michael] ~]> wc -l notation.texi2pdf.log.old
11200 notation.texi2pdf.log.old
michael] ~]> wc -l notation.texi2pdf.log.new
7806 notation.texi2pdf.log.new