Make initial Embed call asynchronous
Make initial Embed call asynchronous

The initial Embed does not need to be synchronous, so set a reply callback
instead.  This prevents a long delay if the registry daemon does not respond.
Also unref some related messages that we were leaking.

Also fix a warning.

GNOME/at-spi2-core,GNOME/at-spi2-core,Distrotech/at-spi2-atk,Distrotech/at-spi2-atk,GNOME/at-spi2-core,GNOME/at-spi2-atk