[racket] does #:scale work in @image?

Scaling wasn't implemented for GIFs, so I've pushed an update.

At Mon, 12 May 2014 18:24:40 -0700, Matthew Butterick wrote:
> According to the docs [1], Scribble's @image command takes a #:scale parameter 
> like so:
> 
> > #lang scribble/manual
> > 
> > @image["foo.gif" #:scale 0.4]
> 
> However, though the 'scale' argument appears in the 'doc exported by the 
> Scribble file, regardless of how I set #:scale, the generated HTML looks like 
> this:
> 
> > <img src="foo.gif" alt=""/>
> 
> 
> So it appears 'scale' is getting dropped during the HTML render ... or is there 
> a wrinkle I'm overlooking? 
> 
> 
> 
> [1] 
> http://docs.racket-lang.org/scribble/base.html#%28def._%28%28lib._scribble%2Fbas
> e..rkt%29._image%29%29____________________
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