added back in phrase-score caching, which cuts runtime for both grammar types by 50--75%
added back in phrase-score caching, which cuts runtime for both grammar types by 50--75%

gwenniger/joshua,thammegowda/incubator-joshua,thammegowda/incubator-joshua,fhieber/incubator-joshua,thammegowda/incubator-joshua,gwenniger/joshua,fhieber/incubator-joshua,lukeorland/joshua,lukeorland/joshua,fhieber/incubator-joshua,thammegowda/incubator-joshua,fhieber/incubator-joshua,fhieber/incubator-joshua,fhieber/incubator-joshua,gwenniger/joshua,thammegowda/incubator-joshua,gwenniger/joshua,lukeorland/joshua,fhieber/incubator-joshua,lukeorland/joshua,thammegowda/incubator-joshua,thammegowda/incubator-joshua,lukeorland/joshua,lukeorland/joshua,thammegowda/incubator-joshua,gwenniger/joshua,lukeorland/joshua,gwenniger/joshua,lukeorland/joshua,thammegowda/incubator-joshua,fhieber/incubator-joshua,lukeorland/joshua,fhieber/incubator-joshua,thammegowda/incubator-joshua