Rearrage bits in first field (after header) of PyLongObject. * Bits 0 and 1: 1 - sign. I.e. 0 for positive numbers, 1 for zero and 2 for negative numbers. * Bit 2 reserved (probably for the immortal bit) * Bits 3+ the unsigned size.

This makes a few operations slightly more efficient, and will enable a more compact and faster 2s-complement representation of most ints in future.