Add Theme function to apply additional resizing

Hello,

I am building a mobile theme for my site and wish to use Image Resize Filter to change the size of embedded images to suit small mobile screens. However, I still wish the standard theme for the site to deliver the original sized images. To allow this I have written the attached patch which adds a function I have called theme_image_resize_filter_scale_factor(). This allows the theme to return a scale factor (such as "0.5") and thus have embedded images delivered at, say, half size.

It would be very helpful if this, or an equivalent, could be incorporated in the released version of the module.

With thanks, Tony

(P.S. I have created the patch under Windows with the Gnu utilities, so I apologise if it is not quite in the format required. I hope this is OK.)