Added IRAF plugin to Ginga

	modified:   AstroImage.py
	modified:   BaseImage.py
	modified:   Callback.py
	modified:   Control.py
	modified:   FitsImage.py
	modified:   FitsImageCanvas.py
	modified:   Mixins.py
	modified:   PythonImage.py
	modified:   ginga.py
	modified:   gtkw/FitsImageCanvasGtk.py
	modified:   gtkw/FitsImageCanvasTypesGtk.py
	modified:   gtkw/FitsImageGtk.py
	modified:   gtkw/GingaGtk.py
	modified:   gtkw/GtkHelp.py
	modified:   gtkw/example2.py
	new file:   gtkw/plugins/IRAF.py
	modified:   gtkw/plugins/Info.py
	modified:   gtkw/plugins/Zoom.py
	new file:   misc/plugins/IIS_DataListener.py
	new file:   misc/plugins/IRAFBase.py
	modified:   qtw/FitsImageCanvasQt.py
	modified:   qtw/FitsImageQt.py
	modified:   qtw/QtHelp.py
	new file:   qtw/plugins/IRAF.py
	modified:   qtw/plugins/Info.py
	modified:   qtw/plugins/Zoom.py

Added a new "IRAF" global plugin to Ginga.
  - Ginga can now act as a ximtool like server and interact with IRAF in the
      same manner as DS9 and IRAF.
  - Understands the IMTDEV environment variable
  - Invoke Ginga with the --modules=IRAF option to enable the plugin
  - See instructions in misc/plugins/IRAFBase

This takes a new approach from the previous plugins to providing the cross
widget support.  It uses a non-gui specific base class (in misc/plugins)
combined with the GUI bits.  Some other plugins may eventually be refactored
to use the approach to speed up development, avoid code bloat and reduce
chance of errors.