Fix bug 4806

Fix bug 4806

	* Context.cpp (begin_layout): make it a (private) method, and output
	the extra stuff here.
	(add_par_extra_stuff): this is used for stuff that is only for next
	paragraph (like extra_stuff used to be); add_extra_stuff is now for
	code that is output for all paragraphs in the context.

	* text.cpp: update to new Context methods. Every user of add_extra_stuff
	uses add_par_extra_stuff, except alignment (which has to be repeated
	to fix bug 4806).

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@24656 a592a061-630c-0410-9148-cb99ea01b6c8