1. Fixed slow-click timer.

1. Fixed slow-click timer.

2. Fix for full cell background to be painted.  (One line on the edges
was showing through to the background.)

3. Added current cell highlight.  Currently it just draws a thick
border using the gridLineColour just inside the cell borders.

4. Make dragging a little less sensitive by ensuring that the mouse
drags at least 3 pixels before anything is done to the grid.

5. CaptureMouse while drag-selecting cells and fixed to make cells
visible if dragging outside window boundaries.  Still a problem here
though, it moves way to fast to see what's happening (at least on MSW.)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@6002 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775