Revert "Get rid of c_[u]long BigInt constructors."

This reverts commit d2883092b4be1fa14e21ee17461801d6b79c535a.
Revert "Add additional BigInt constructors for [u]int(64) args (where c_[u]long is expected)."

This reverts commit a87aca1209179319c83990de9654b2c73141548b.