Optimize drawing.
* BufferView:
- update(): returns a pair of bools in order to inform for singlePar cases.
- workAreaDispatch(): ditto and simplify the logic by using cursor update flags.
* text.C
- breakParagraph(): change the cursor update flag as needed.
- insertChar(): ditto.
- erase(): ditto
- redoParagraph(): now returns true if there is a height change.
* text3.C: dispatch():
- initialize the cursor flag at the beginning
- LFUN_MOUSE_PRESS: no need to update.
- LFUN_MOUSE_RELEASE: ditto.
- add some FIXMEs and comments.
* LyXFunc::dispatch(): simplify the BufferView update.
* insets/insetcollapsable.C: clarify and simplify the logic in doDispatch().
* WorkArea::dispatch(): redraw only if needed.
git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@15958
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