Attempt #2 at proper multiplatform distillation for pants.pex.
Ensure an ensemble expands to a unique set of ips.
Merge pull request #138 from jsirois/jsirois/zk/ensure_unique_ips

Ensure an ensemble expands to a unique set of ips.
Use an older 10 series mactel platform for maximum compatibility.
Fixup SourceTranslator to refuse translation for anything but the current platform and python.
Turn on verbose mode for common:all tests.
Merge pull request #137 from jsirois/jsirois/open_multiplatform

Rig up multi-platform pants.pex in the open as a stop-gap