Make the pixel formats which were defined as macros:
defined as enum PixelFormat values, and viceversa make:
defined as macros, also resort accordingly the enum PixelFormat
Also make avcodec_get_pix_fmt() recognize the "rgb32" and "bgr32"
aliases, in order to make ffmpeg pass regressions test.
This change breaks ABI backward compatibility.
Originally committed as revision 18163 to svn://svn.ffmpeg.org/ffmpeg/trunk