preserve type information of wrapped exception when constructing a
ForeignException. this requires using `std::current_exception` for
construction in all cases as passing the exception by reference to
any function erases dynamic type information: `throw` may copy the
thrown exception from its source expression; this only works as we
need it to if static and dynamic type of the expression are equal.
fixes#1000
Change-Id: I7167f298540de7c43c2566592bdb8d7a93c34d31
