bug#6839: 24.0.50; heuristic mask is turned on on gif images willy-nilly

[Katsumi Yamaoka]

Katsumi Yamaoka wrote:
> Some gif images' background will be made transparent.
> Please try this:

> emacs -Q -bg black -fg white scholartest2009.gif

> Where the gif file is:

> http://mainichi.jp/life/edu/scholartest/etc/image/scholartest2009.gif

> It is due to `create-animated-image' that puts the heuristic mask
> property to gif images unconditionally.  image-mode uses it.
> Is it intentional?  I hope the `:mask heuristic' element is removed
> from `create-animated-image'.

I did it by myself.  Thanks.

> Emacs-w3m uses `create-animated-image' if it is available, instead
> of `create-image'.  It causes some gif images to be transparent.