Merge release 0.15.15 from branch 'v0.15.x'

Conflicts:
	NEWS
	configure.ac

src/input/rewind_input_plugin.c

@@ -81,7 +81,7 @@ copy_attributes(struct input_rewind *r)
 	const struct input_stream *src = r->input;
 
 	assert(dest != src);
-	assert(dest->mime != src->mime);
+	assert(src->mime == NULL || dest->mime != src->mime);
 
 	dest->ready = src->ready;
 	dest->seekable = src->seekable;