ambigous conversion for autoPtr<bool>

The autoPtr currently has different casting types. Eg,

explicit operator bool() const noexcept;
operator const T&() const;

Consider the following:

autoPtr<bool> something;

if (something) ...

This may either imply that the operator bool is invoked (testing for existence of the pointer), or the operator const T& is invoked (returning the value of the pointer).

The casting to type is not particularly desirable, but still supported with #define Foam_autoPtr_castOperator in order to handle legacy code.

Current best fix is to replace with Switch.