This commit removes the needRedraw() interface and simplify the screen update procedu...

This commit removes the needRedraw() interface and simplify the screen update procedure. It also fixes all crash problems.
The performance may suffer a bit because we do the second drawing step in all cases. This could be possibly optimized out by checking the return value of the BufferView::update() method in "lyxfunc.C:1610". But it is maybe better to keep those two parts of the frontend ignorant of each other: the event handling and the drawing.

BufferView:
* needRedra(), need_redraw_: deleted.
* updateMetrics(): now public.
* update(): only do the first drawing step. Returns true if a full updateMetrics is needed before drawing on screen.

WorkArea:
* redraw(): no check on BufferView::needRedraw(), call updateMetrics() unconditionally.
* processKeySim(): uneeded "redraw()" call commented out. When/if the call to LyXView::redrawWorkArea() in "lyxfunc.C:1610" is not needed anymore, this line should be uncommented out.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@14456 a592a061-630c-0410-9148-cb99ea01b6c8