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

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@11061 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

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)\