libx264: list possible profiles.

The values are listed if setting them fails.
Using "-profile help" or "-profile list" have that effect.
Similar to 3aba391f.
Suggested by "rogerdpack" in trac ticket #1529.

libavcodec/libx264.c

@@ -447,7 +447,12 @@ static av_cold int X264_init(AVCodecContext *avctx)
 
     if (x4->profile)
         if (x264_param_apply_profile(&x4->params, x4->profile) < 0) {
+            int i;
             av_log(avctx, AV_LOG_ERROR, "Error setting profile %s.\n", x4->profile);
+            av_log(avctx, AV_LOG_INFO, "Possible profiles:");
+            for (i = 0; x264_profile_names[i]; i++)
+                av_log(avctx, AV_LOG_INFO, " %s", x264_preset_names[i]);
+            av_log(avctx, AV_LOG_INFO, "\n");
             return AVERROR(EINVAL);
         }