Broken backward compability: libBoost 1.66 -> libBoost 1.67 #74

Problematic code:

#include <boost/optional/optional.hpp>

struct A
{
    A(int a) : a(a) {}

    int a;
};

 #define TRUE 1

int main()
{
    return boost::optional<A>(TRUE , 5)->a;
}

libBoost 1.66 calls here:
optional ( bool cond, rval_reference_type val )
boost::optional(1, A(5));
and returns 5,

libBoost 1.67 and newer calls here:
template
explicit optional ( Expr&& expr,
BOOST_DEDUCED_TYPENAME boost::enable_if< optional_detail::is_optional_val_init_candidate<T, Expr>, bool>::type = true
)
and returns 1.

This is change of behavior without any warring.