archive: close archive when stream is closed

Fixes a memory leak: the "archive" input plugin opens the archive, but
never closes it.  This patch moves the responsibility for doing that
to archive_plugin.open_stream().  This is an slight internal API
change, but it is the simplest and least intrusive fix for the memory
leak.

src/archive/bz2_plugin.c

@@ -173,6 +173,8 @@ bz2_is_close(struct input_stream *is)
 	bz2_context *context = (bz2_context *) is->data;
 	bz2_destroy(context);
 	is->data = NULL;
+
+	bz2_close((struct archive_file *)context);
 }
 
 static int