(bug 28762) Resizing to specified height broken for very thin images

(bug 28762) Resizing to specified height broken for very thin images

Restructure and comment of ImageHandler::normaliseParams(). ImageHandler::normaliseParams() will now output both width/height as physicalWidth/Height, where width/height are the dimensions used by the browser, and physicalWidth/Height are the dimensions of the thumbnail that will be created. This allows keeping the use of unique dimensions for a specified thumbnail width, by forcing client side resizing of 1px-wide images with non corresponding height.
Also fixed a bug where the check for mustRender() was in an if statement where it should not have been.