export (e.g. the ToC) and the navigate menu.
* src/insets/insetbase.h
(InsetBase::plaintext): output to a docstream
(InsetBase::textString): ditto
* src/mathed/TextPainter.h
(TextPainter::show): ditto
* src/support/docstream.[Ch] New file and string streams for
docstring. The file streams convert to UTF8 on the fly.
* many more files: Adjust to the changes above
git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@15301 a592a061-630c-0410-9148-cb99ea01b6c8
