Fix for broken RGB loader
Fix for broken RGB loader

- seek() function in Pillow does not seem to work as we expect
- also fixed an issue saving JPEG files from RGBA images

ejeschke/ginga,naojsoft/ginga,pllim/ginga,pllim/ginga,naojsoft/ginga,ejeschke/ginga,ejeschke/ginga,naojsoft/ginga,pllim/ginga