add FFMIN3

Originally committed as revision 12982 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/common.h

@@ -113,6 +113,7 @@
 #define FFMAX(a,b) ((a) > (b) ? (a) : (b))
 #define FFMAX3(a,b,c) FFMAX(FFMAX(a,b),c)
 #define FFMIN(a,b) ((a) > (b) ? (b) : (a))
+#define FFMIN3(a,b,c) FFMIN(FFMIN(a,b),c)
 
 #define FFSWAP(type,a,b) do{type SWAP_tmp= b; b= a; a= SWAP_tmp;}while(0)