Clarify comment block and rewrite in better English.

Originally committed as revision 10837 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mpegvideo.c

@@ -843,17 +843,17 @@ int ff_find_unused_picture(MpegEncContext *s, int shared){
     }
 
     av_log(s->avctx, AV_LOG_FATAL, "Internal error, picture buffer overflow\n");
-    /*we could return -1 but the codec would crash anyway, trying to draw
-      into, a non existing frame, this is safer than waiting for a random crash
-      also the return of this is never usefull, a encoder must only allocate
-      as many as allowed in the spec which has no relation to how many lavc
-      could allocate (and MAX_PICTURE_COUNT is always large enough for such
-      valid streams)
-      and a decoder has to check stream validity and remove frames if too many
-      reference frames are around. waiting for "OOM" is not correct at all, it
-      similarely has to replace missing reference frames by (interpolated/MC)
-      frames anything else is a bug in the codec ...
-    */
+    /* We could return -1, but the codec would crash trying to draw into a
+     * non-existing frame anyway. This is safer than waiting for a random crash.
+     * Also the return of this is never useful, an encoder must only allocate
+     * as much as allowed in the specification. This has no relationship to how
+     * much libavcodec could allocate (and MAX_PICTURE_COUNT is always large
+     * enough for such valid streams).
+     * Plus, a decoder has to check stream validity and remove frames if too
+     * many reference frames are around. Waiting for "OOM" is not correct at
+     * all. Similarly, missing reference frames have to be replaced by
+     * interpolated/MC frames, anything else is a bug in the codec ...
+     */
     abort();
     return -1;
 }