ImageItem now has auto downsampling; seems to be working properly.
Still need auto clipping as well.
Update imageToArray to support Py2.6 + Qt 4.10
pg.dbg() now returns pointer to console widget
Added automatic image downsampling (disabled by default)
  - Reduces aliasing when zoomed out
  - Improves performance and memory usage for large images
Merge branch 'image_downsampling' into develop

Conflicts:
	pyqtgraph/graphicsItems/ImageItem.py
Added GLViewWidget.setBackgroundColor()
Add check for even array length when using arrayToQPath(connect='pairs')