string review: Merge/canonicalize debug string messages.

still some  printfs in dvbsub.c. Would  need to spend some  time reading
the code to remove them.

RGB2 sorta works, but to do better we need a way to lookup a palette
color in a colormap.

Render->Blend

and work done to allow for palettized rendering (by not expanding
inline colormap entries when RGB2).

Started RV32 and- has bugs. (It'd be nice if something in rendering
worked the first time without a hassle).

Modules.am, pixmap.h, subtitle.h: Some of the pixel stuff has been
moved here.

cvd.c: remove option duplicated with ogt.c Probably should be hoisted more
to a main routine. Perhaps if spudec is folded in.

chroma does the scaling.

(4:3 is one of the few *not* in this category).

Allow user to override subtitle scaling via sub-aspect-ratio, 0=auto
or what we do now. 1=do nothing.

* modules/codec/ogt/*: win32 compilation fixes.

{cvd,ogt}_parse.c, common.c, subtitle.h: add ability to dump subtitles via
libpng.

some cleanup.