Two plugin-rework patches

[Ray Strode]

Hi,

> The difference being that any partially transparent parts of the overlay
> frames will be drawn twice (although not as strongly the second time) and
> thus receive a double dose of the partly transparent foreground colour. On
> the filling circle, the only parts this effects is the edges which throb as
> there is a sudden step between showing two superimposed images and a single
> image. You can only see it properly in the last frames of the filling
> sequence.
Oh that makes sense.  Yea, please push it.  Thanks!

At some point i'd like to move all the pixel munging functions (like
bluring, blending, the halo thing in solar) to convenience functions
so each plugin doesn't have to do it itself.

On a different note, I think at some point it may make sense to merge
parts of ply_image and ply_frame_buffer into a new ply_pixel_buffer.

At the end of the day both things are just pixels after all and it
would be useful if there was a common interface for manipulating those
pixels.  Also, having to do

ply_image_get_data() all the time just to feed it back into the
framebuffer is less than ideal.

Anyway, thanks for the review and fixes.

--Ray