[Merge] lp:~thomas-voss/dbus-cpp/fix-potential-race-with-callback-invocation into lp:dbus-cpp

[Marcus Tomlinson]

If I were to be super pedantic, the PendingCall class could do with a test for cancel(), but its just a redirect so I can't imagine it blowing up.
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https://code.launchpad.net/~thomas-voss/dbus-cpp/fix-potential-race-with-callback-invocation/+merge/237224
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