* Beginning of the built-in modules support.

   A few words about the changes:

  - heavy Makefile butchery has taken place, each plugin now has its own
    Makefile. I know recursive make blablah harmful, but it was just so
    much easier to do this way.

  - Makefile.in has disappeared, we now generate Makefile.opts with
    the overall configuration options, and Makefile.modules which is
    specific to module compilation.

  - After ./configure has been run you may want to modify Makefile.opts
    to check which modules will be compiled built-in or as plugins.

  - Some modules cannot be compiled built-in right now because proper
    linkage doesn't work yet. We don't really care since they're the
    interface or video output modules. The most important stuff works
    (iDCT, motion, YUV, input).

  - It's perfectly valid to compile a module both as built-in and as a
    plugin. vlc will only load the built-in one, but I'll add an option
    to ignore built-in modules for testing purposes.

  - We *should* see a performance increase here. I didn't have much time
    to test it, but if anyone can confirm and perhaps give a rough
    estimate of how much we gain...