Forgot to include config.h
cleanup: remove a few bogus comment lines
Implement 'conversion' as a future replacement for 'SelectType'

The C++11 standard library offers the functionality of SelectType,
it is, however, called 'conditional'.  This patch adds a copy
of our SelectType implementation with the class names changed
to match the ones used in C++11.  The old SelectType implementation
gets deprecated.
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