Code review comment for lp:~aacid/qtmir/fix_clang_build

This doesn't quite do the same thing as the original code. My alternative fix was:

- using PromptSessionListener::PromptSessionListener;
+ using ::PromptSessionListener::PromptSessionListener;

Which provides a PromptSessionListenerImpl::PromptSessionListenerImpl(QObject* = 0) constructor (which is Qt style as I understand it).

But that ctor could be re-introduced if ever needed.