Bug fixes and updates to Ginga FITS viewer

	modified:   AstroImage.py
	modified:   AutoCuts.py
	modified:   BaseImage.py
	modified:   Control.py
	modified:   FitsImage.py
	modified:   LICENSE.txt
	modified:   Mixins.py
	modified:   PythonImage.py
	modified:   Settings.py
	modified:   ginga.py
	modified:   gtkw/FitsImageGtk.py
	modified:   gtkw/GingaGtk.py
	modified:   gtkw/GtkHelp.py
	modified:   gtkw/Plot.py
	modified:   gtkw/example1.py
	modified:   gtkw/example2.py
	modified:   gtkw/plugins/Cuts.py
	modified:   gtkw/plugins/FBrowser.py
	modified:   gtkw/plugins/Histogram.py
	modified:   gtkw/plugins/Info.py
	modified:   gtkw/plugins/Pan.py
	modified:   gtkw/plugins/PixTable.py
	modified:   gtkw/plugins/Thumbs.py
	modified:   gtkw/plugins/Zoom.py
	modified:   qtw/FitsImageQt.py
	modified:   qtw/GingaQt.py
	modified:   qtw/Plot.py
	modified:   qtw/QtHelp.py
	modified:   qtw/example1.py
	modified:   qtw/example2.py
	modified:   qtw/plugins/FBrowser.py
	modified:   qtw/plugins/Histogram.py
	modified:   qtw/plugins/Pan.py
	modified:   qtw/plugins/Thumbs.py

- fixed a bug where scipy.pilutil was being imported without catching an
    ImportError
- fixed a regression of the Histogram plugin
- improved Histogram plugin to show the cut levels graphically and to allow
    the user to set cut levels or auto levels from the plugin
- small fixes to set background and allow rotation in example programs
- fixed a bug where the Pan image could be accidentally moved by trying to
    pan in the pan image itself
- Thumbs plugin now has a feature where it can cache thumbnails to disk
  - (not enabled by default and currently no UI to allow it--this is coming soon)