Set global header flag for every container that requires it.

Patch by Art Clarke a$(name) xuggle com

Originally committed as revision 17425 to svn://svn.ffmpeg.org/ffmpeg/trunk

output_example.c

@@ -224,7 +224,7 @@ static AVStream *add_video_stream(AVFormatContext *oc, int codec_id)
         c->mb_decision=2;
     }
     // some formats want stream headers to be separate
-    if(!strcmp(oc->oformat->name, "mp4") || !strcmp(oc->oformat->name, "mov") || !strcmp(oc->oformat->name, "3gp"))
+    if(oc->oformat->flags & AVFMT_GLOBALHEADER)
         c->flags |= CODEC_FLAG_GLOBAL_HEADER;
 
     return st;