bug#71909: 30.0.60;

[Cecilio Pardo <cpardo@imayhem.com>]

>> The image conversion is done using GdiPlus functions, which are
>> already used on w32image.c, but are static. I have splitted this file
>> into .c and .h, to be able to reuse those definitions. The image
>> conversion requires that native image functions are activated.
> 
> What happens with yank-media if the user disables native image APIs?
> Do we signal an error or is there some graceful degradation (like
> using another MIME type)?

The ability to yank DIBV5 will be lost. If there is no alternative such 
as PNG or image/*, then yank can't be done.

> Why a unibyte string?  Is this always binary data or something?  If
> this could be text (e.g., text/html), then a unibyte string is not the
> best choice.

It can be binary, but not always.  Is unibyte ok for binary cases? I can 
treat text/* differently, and make exceptions for types like image/svg+xml.

> In any case, if the function must return a unibyte string in some
> cases, that should be mentioned in the doc string, because callers
> will otherwise not expect to get a unibyte string.  Also, where will
> this unibyte string be decoded?

In the binary case, is there any decoding to do?