lavu: add an API function to return the FFmpeg version string

This returns something like "N-73264-gb54ac84". This is much more useful
than the individual library versions, of which there are too much and
which are very hard to map back to releases or git commits.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/utils.c

@@ -30,6 +30,11 @@
 #include "libavutil/ffversion.h"
 const char av_util_ffversion[] = "FFmpeg version " FFMPEG_VERSION;
 
+const char *avutil_version_info(void)
+{
+    return FFMPEG_VERSION;
+}
+
 unsigned avutil_version(void)
 {
     static int checks_done;