Add high dpi images for the ribbon to use: specifying these should help with startup time in high-dpi mode since the images don't have to be resized by MFC.

git-svn-id: http://tortoisesvn.googlecode.com/svn/trunk/src/TortoiseMerge@24281 4cfb86a4-2c7a-11df-bd14-c1e331e6ceac