Try Configure again (take a million)

Now all detection / config loading is done *inside* the Configure command.
It should hopefully be a little bit easier to follow the order of events.

All build / conf / temp files should be written in build_base (see #318)

Should also address the issue of requiring `setup.py build bdist_egg` in order to get bundled libzmq.dylib into the tree.

Back to the VMs for testing...

- [x] OS X no libzmq specified, libzmq present
- [x] OS X, no libzmq specified, libzmq not present (fallback to extension)
- [x] OS X libzmq specified
- [x] OS X libzmq-extension requested
- [x] OS X bdist_egg (check rpath)

- [x] Win no libzmq specified, libzmq not present (fallback to extension)
- [x] Win libzmq specified
- [x] Win libzmq-extension requested
- [x] Win bdist_egg

- [x] Linux, not specified, libzmq present
- [x] Linux no libzmq specified, libzmq not present (fallback to extension)
- [x] Linux libzmq specified
- [x] Linux libzmq-extension requested
- [x] Linux bdist_egg

- [x] BSD no libzmq specified, libzmq not present (fallback to extension)
- [x] BSD libzmq specified
- [x] BSD libzmq-extension requested
- [x] BSD bdist_egg