Add 'quit' command to TestShell.
Fix TestShell shutdown.

Place most of the loop inside a try block - this is what we want generally,
but for shutdown we /definitely/ need to catch the ReaderError thrown when
the read() is interruted.

Also, fix unreleased mutex by adopting AutoMutex.
Merge branch 'master' of ssh://core.linn.co.uk/home/git/ohnet
Prevent premature exit from main() in Os/Core/Main.cpp