Replace deprecated setFlipped: method calls
Ignore userdata directories
Improve column width resizing performance

Only invalidate the relevant part of the content and header views. Invalidate
the column width cache at the proper time so it doesn't lag behind the mouse.
This took a while to figure out...
Extract attributed string creation into attributedStringValue method

This was just done as cleanup while working on performance fixes
Merge pull request #16 from RobotsAndPencils/DragPerformanceAndGlitches

Column resize performance