Two plugin-rework patches

[Charlie Brej]

test.patch has some additional lines to the makefiles to allows the tests 
compile. (ply-list.c/h were needed whenever ply-logger was used and 
DPLYMOUTH_PLUGIN_PATH were needed by boot_splash_test)

fade.patch is a review request as I am unsure about a couple things. It creates 
a new image data block with the fade being done by weighting the data from each 
image. This is then drawn on the screen.
Firstly it breaks progress_animation->transition type choice as there isn't one 
any more. Secondly I am unsure why when transitioning between images of 
different sizes but keeping a single frame_area didn't draw squiggles across the 
area. Its probably OK, but better just check if I have the right end of the stick.
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