Fixed a bunch of bugs that came up when integrating with mySQL again.

Thanks Matthijs!

tests/PreparedTest.cpp

@@ -90,6 +90,7 @@ int main()
 	{
 		auto s = select(all_of(t)).from(t).where(t.beta.like(parameter(t.beta)) and t.alpha == parameter(t.alpha) or t.gamma != parameter(t.gamma));
 		auto p = db.prepare(s);
+		p.params.alpha = 7;
 		using S = decltype(s);
 		using T = sqlpp::make_parameter_list_t<S>;
 		T npl;