Fixed an issue with the glBlendingMode that was causing the result to be pre-multiplied twice.
Fixed an issue that was causing images that have a data window that is wider than the display window but with matching heights to be entirely rendered when areas outside of the display window should be greyed out.
Changed the minimum filter to GL_LINEAR for the image viewer.
Moved the glBlendFunc into the renderImage method.
Removed the texture filter arg from StandardStyle::RenderImage().
Added the texture filtering to a scope within ImageView::doRender.
Merge pull request #268 from goddardl/ViewerFix

Merging this to get it in the next tag. Luke will keep thinking about how to test, and John may come back with more changes.