Merge branch 'xelatex' into doc/4.9

Mauro says:

	This patch series fix Sphinx to allow it to build the media
	documentation as a PDF file.

	The first patch is actually a bug fix: one of the previous patch
	broke compilation for PDF as a hole, as it added an extra
	parenthesis to a function call.

	The second patch just removes a left over code for rst2pdf.

	The other patches change from "pdflatex" to "xelatex" and address
	several issues that prevent building the media books.

	I think this patch series belong to docs-next. Feel free to merge
	them there, if you agree. There's one extra patch that touches
	Documentation/conf.py, re-adding the media book to the PDF build,
	but IMHO this one would be better to be merged via the media tree,
	after the fixes inside the media documentation to fix the build.