Return the same results of GMP >= 4.2.
This allows cross-type hash joins of these types together. Note that cross-type hash join can't be used yet as we need to set up an operator family. However an eventual hash index created now wouldn't be broken if we want to add this feature later.
PG 8.3 is missing other functions. Because current Ubuntu installs 8.4, supporting this version is already a good step.