Setting MACOSX_DEPLOYMENT_TARGET on Darwin

This is fix for #219 and #220, with fixing/adding some tests.

If the build is for universal (if `--enable-universalsdk` has found in `PYTHON_CONFIGURE_OPTS`), this also sets `--with-universal-archs=intel` as configure option of CPython. This is as same method as building universal binary with saghul/pythonz and python formula of Homebrew.