Under certain conditions QObject::connect can deadlock.

Steps to reproduce:

• Launch the attached example application
• Let it run for a while until it will print out "Deadlock detected"

Application workflow:
1) Worker thread is started.
2) Work is done, emit is called with argument Foo. Foo will connect signals when it is copy-constructed.
3) In the emit call, Foo is copy-constructed and connect is called.
4) Deadlock, emit call never returns.