* Renamed `cast-flonum-to-integer' to `cast-ieee754-double-to-integer'.

* Renamed `cast-flonum-to-integer' to `cast-ieee754-double-to-integer'.

* Renamed `cast-integer-to-flonum' to `cast-integer-to-ieee754-double'.

* Changed both to use <uint64_t> instead of <unsigned long> for
conversion.  That way, they should work on 32-bit systems.  (Thanks to
Taylor for pointing out that bug.)

* Added `cast-ieee754-single-to-integer' and `cast-integer-to-ieee754-single'.

* Updated existing tests.

* Added tests for casts to and from single-precision floating-point numbers.