Move log_callback_help to cmdutils.[hc], for allowing sharing.

Originally committed as revision 25149 to svn://svn.ffmpeg.org/ffmpeg/trunk

cmdutils.h

@@ -44,6 +44,12 @@ extern AVCodecContext *avcodec_opts[AVMEDIA_TYPE_NB];
 extern AVFormatContext *avformat_opts;
 extern struct SwsContext *sws_opts;
 
+/**
+ * Trivial log callback.
+ * Only suitable for show_help and similar since it lacks prefix handling.
+ */
+void log_callback_help(void* ptr, int level, const char* fmt, va_list vl);
+
 /**
  * Fallback for options that are not explicitly handled, these will be
  * parsed through AVOptions.