Unsets the NV/IV status of an SV.
=for apidoc Am|bool|SvOK|SV* sv
-Returns a boolean indicating whether the value is an SV.
+Returns a boolean indicating whether the value is an SV. It also tells
+whether the value is defined or not.
=for apidoc Am|bool|SvIOKp|SV* sv
Returns a boolean indicating whether the SV contains an integer. Checks