Fix for building with VS2013.
Two fixes with SVG rasterizing:
1. Original width/height were being returned as integers, even though they can be floats (see SVGResource::getImageSize()).  Function also renamed to be more descriptive (renamed to getSourceImageSize()).
2. Now we always round height and scale width from the rounded height when doing scaling, since SVG rasterization scale is determined from height. This seems to fix some 1px cutoff I was seeing, but I'm not sure if it still works for images with extreme aspect ratios that are taller rather than wider.