Bug 1232580 - Install py27-readline on MacPorts; r=Yoric

See https://trac.macports.org/ticket/48807. Without it, reading
input can break terminals.

--HG--
extra : rebase_source : 7eab1e60d6a6279fdaf25a4789598cf96e2b8d6c

python/mozboot/mozboot/osx.py

@@ -388,6 +388,7 @@ class OSXBootstrapper(BaseBootstrapper):
     def ensure_macports_system_packages(self):
         packages = [
             'python27',
+            'py27-readline',
             'mercurial',
             'autoconf213',
             'gnutar',