Clarify PIX_FMT_BE flag doxy. Increase consistency / pickiness.

Originally committed as revision 20592 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/pixdesc.h

@@ -84,7 +84,7 @@ typedef struct AVPixFmtDescriptor{
     AVComponentDescriptor comp[4];
 }AVPixFmtDescriptor;
 
-#define PIX_FMT_BE        1 ///< big-endian
+#define PIX_FMT_BE        1 ///< Pixel format is big-endian.
 #define PIX_FMT_PAL       2 ///< Pixel format has a palette in data[1], values are indexes in this palette.
 #define PIX_FMT_BITSTREAM 4 ///< All values of a component are bit-wise packed end to end.
 #define PIX_FMT_HWACCEL   8 ///< Pixel format is an HW accelerated format.