Removed old, unused Makefile
Merge remote-tracking branch 'origin/master'
Fixed some bugs relating to the generation of thumbnails

	modified:   README.txt
	modified:   ginga/Control.py
	modified:   ginga/FitsImage.py
	modified:   ginga/doc/INSTALL-Linux.txt
	modified:   ginga/doc/INSTALL.txt
	modified:   ginga/gtkw/FitsImageGtk.py
	modified:   ginga/gtkw/plugins/Thumbs.py
	modified:   ginga/misc/Settings.py
	modified:   ginga/qtw/FitsImageQt.py
	modified:   ginga/qtw/plugins/Thumbs.py

- fixed a bug where not all thumbnails would be generated if multiple
    files were dropped on the window
- disabled automatic strolling to the bottom of the thumbs pane when new
    thumbs are added
- suppressed an error where a divide-by-zero error is generated on a blank
    image
- updated documentation slightly to reflect new distutils-based installation