Improve parse_primary() error message.

Patch by Stefano Sabatini and Michael Niedermayer


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@13218 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavcodec/eval.c

@@ -217,7 +217,7 @@ static AVEvalExpr * parse_primary(Parser *p) {
 
     p->s= strchr(p->s, '(');
     if(p->s==NULL){
-        *p->error = "missing (";
+        *p->error = "undefined constant or missing (";
         p->s= next;
         ff_eval_free(d);
         return NULL;