Support synchronous out-parameters in async methods
There are methods even in gio-2.0, like DBusConnection.send_message_with_reply(), which have out-parameters in there "begin" methods which vala is currently not able to handle.
For bindings there is a workaround by simple using converting such parameters to pointers. This workaround was pushed as dd304f4d
See #636 (closed)
Some ideas at !3