Added a 32-bit add example.

This is useful in simple debugging cases. Given it's a 32-bit input circuit the circuit is constructed in one big chunk instead of multiple chunks along the way (i.e., the PCF2 compiler does not appear to assign all input gates adjacent wire ids in larger circuits). This, along with the bxor, band, bor, make for good simple correctness tests for third party garbled circuit file formats.