Signals from Objects exported via ExportChildObjects are not emitted over DBus

If an object is exported on D-Bus via ExportChildObjects, and that object emits a signal, the signal emission is not transmitted over D-Bus.

I can confirm that using the ExportAllSignals flag doesn't make a difference.

For clarity, to reproduce the bug, start ./master first, then start ./slave. 5 seconds after starting master, the child object will emit a fooChanged signal. The slave is listening for that signal, but the connected slot is not invoked.