Workaround is for ViewBox to see whether its scene has changed every time it paints.

Fixes: 12

temporary fix for text parameter ignoring expanded option
Don't use os.EX_OK in pg.exit()

cleaned up examples

  - generalized makeARGB API: can now process arrays of arbitrary shape.
  - affineSlice automatically converts vector arguments to array
  - new function applyLookupTable taken from makeARGB
  - isosurface function returns array
Updated VideoSpeedTest example to follow new makeARGB API

LayoutWidget: row argument now accepts 'next' as value
ParameterTree bugfix: avoid infinite recursion when accessing non-existent attributes
ViewBox: avoid exit error caused when cleanup callback is invoked while python is shutting down

Now detects and switches between PyQt / PySide automatically; no need to distribute different versions of the library anymore.

minor updates for other examples

 - HistogramLUTItem avoids using lookup table if possible
 - GradientEditorItem has a method to ask whether the gradient is trivial (can be applied without the use of a lookup table)
 - ROI, LinearRegionItem, InfiniteLine no longer redraw for every mouse movement