This patch implements proper ERT behaviour for normal layouts.

This patch implements proper ERT behaviour for normal layouts.
In particular, it makes paragraph breaks generate single \n in latex output
when ParbreakIsNewline is true

This means that it is not necessary anymore to use newlines to break lines.
Plain paragraph breaks can be used instead, like is done now in ERT/Listings.
This is mainly aimed at sweave support.

lyx2lyx support courtesy of Richard Heck

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@36163 a592a061-630c-0410-9148-cb99ea01b6c8