Extracted from r14281

Extracted from r14281

* frontends/LyXView:
	- redrawWorkArea(): new temporary method called from within
	  BufferView::pimpl::update() that calls WorkArea::redraw()
	  in order to do the actual screen redrawing.
* frontends/WorkArea:
	- the redraw() method now check if the the attached bufferView
	  needs a screen redraw().
* BufferView:
	- needsRedraw(): new method for WorkArea::redraw()

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@14381 a592a061-630c-0410-9148-cb99ea01b6c8