osx: wire up genosxversion script The only version strings that are changed are the ones baked into the .pkg - hg's self-reported version string doesn't change, so users will still see our mostly-pip-compatible version strings. For reference, the part of our versioning setup that's not PEP440 compatible is the RC releases - those should be .rc0 insted of -rc. It's too late to change that for the 4.3 cycle, so I'll worry about fixing that during the 4.4 cycle.