1. crash when deleting multi line selection fixed

1. crash when deleting multi line selection fixed
2. BreakLine() does just discard the first line (wreaking total havoc) any
   more
3. ScrollToCursor() actually scrolls to cursor
4. style change affects the first line too - and since the first time, style
   doesn't change mysteriously any more after second Clear()
5. word cursor movement even better (did I get it right this time?)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@2766 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775