src/Text/Pandoc/Writers/LaTeX.hs: Use \texorpdfstring for section
captions.
Update tests suite to expect \texorpdfstring.
Merge branch 'use-texorpdfstring' of https://github.com/wilx/pandoc into wilx-use-texorpdfstring

Conflicts:
	src/Text/Pandoc/Writers/LaTeX.hs
	tests/Tests/Writers/LaTeX.hs
Improved texorpdfstring patch #1148.

* Make LaTeX reader recognize texorpdfstring.
* Don't use texorpdfstring unless it's actually needed.
* Fix tests.