avconv: rename OutputStream.opts to OutputStream.encoder_opts

This makes it more clear what is this variable for exactly.
diff --git a/avconv_opt.c b/avconv_opt.c
index 22f598e..f400e75 100644
--- a/avconv_opt.c
+++ b/avconv_opt.c
@@ -894,7 +894,7 @@
         AVIOContext *s = NULL;
         char *buf = NULL, *arg = NULL, *preset = NULL;
 
-        ost->opts  = filter_codec_opts(o->g->codec_opts, ost->enc->id, oc, st, ost->enc);
+        ost->encoder_opts  = filter_codec_opts(o->g->codec_opts, ost->enc->id, oc, st, ost->enc);
 
         MATCH_PER_STREAM_OPT(presets, str, preset, oc, st);
         if (preset && (!(ret = get_preset_file_2(preset, ost->enc->name, &s)))) {
@@ -909,7 +909,7 @@
                     exit_program(1);
                 }
                 *arg++ = 0;
-                av_dict_set(&ost->opts, buf, arg, AV_DICT_DONT_OVERWRITE);
+                av_dict_set(&ost->encoder_opts, buf, arg, AV_DICT_DONT_OVERWRITE);
                 av_free(buf);
             } while (!s->eof_reached);
             avio_close(s);
@@ -921,7 +921,7 @@
             exit_program(1);
         }
     } else {
-        ost->opts = filter_codec_opts(o->g->codec_opts, AV_CODEC_ID_NONE, oc, st, NULL);
+        ost->encoder_opts = filter_codec_opts(o->g->codec_opts, AV_CODEC_ID_NONE, oc, st, NULL);
     }
 
     avcodec_get_context_defaults3(st->codec, ost->enc);
@@ -1565,7 +1565,7 @@
     unused_opts = strip_specifiers(o->g->codec_opts);
     for (i = of->ost_index; i < nb_output_streams; i++) {
         e = NULL;
-        while ((e = av_dict_get(output_streams[i]->opts, "", e,
+        while ((e = av_dict_get(output_streams[i]->encoder_opts, "", e,
                                 AV_DICT_IGNORE_SUFFIX)))
             av_dict_set(&unused_opts, e->key, NULL, 0);
     }