In Python 3 different opcodes are used for pickling integers with protocol 1 and higher. But pickling with protocol 0 always uses the LONG opcode. In Python all such integers are unpickled to the long instances.

Proposed PR makes integers that fit in a signed 32-bit integer be pickled with the INT opcode. This will decrease the size of a pickle (minus one byte 'L' per integer), speeds up pickling and unpickling, and makes these integers be unpickled to int instances in Python 2, that will save a memory.