Now the Outliner can be scrolled horizontally too. This was the first patch I ever submitted, but it's gone through many revisions due to ugly Blender bugs that needed to be fixed.
Code Notes:
* I discovered an ancient bug which would cause Blender to hang when loading a file saved with horizontal scrollbars turned on for the Outliner/OOPS.
* Therefore, I've added special B_SCROLLO and HOR_SCROLLO defines for use by the Outliner only. These are used in place of B_SCROLL and HOR_SCROLL so that older Blender's won't choke on this stuff. Thanks for this suggestion Ton.
* The hanging occurred in draw_scroll in draw_ipo.c
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