Generate a linking error if perror() is used in libav*

Originally committed as revision 11061 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/internal.h

@@ -257,6 +257,8 @@ if((y)<(x)){\
 #define printf please_use_av_log
 #undef  fprintf
 #define fprintf please_use_av_log
+#undef  perror
+#define perror please_use_av_log_instead_of_perror
 #endif
 
 #define CHECKED_ALLOCZ(p, size)\