A failed attempt to add a new sqlite3_result_zeroterminated() interface that

A failed attempt to add a new sqlite3_result_zeroterminated() interface that
is a hint to SQLite that a TEXT result does have a zero terminator.  The idea
is to avoid unnecessary copying of TEXT values. This seems like an
unnecessary complication at the moment, but maybe I'll return to this later.
Note that this check-in does not work - it is a proof of concept only.

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