add SentenceContext::get_sentence_ptr to allow acces to the senetnce...

add SentenceContext::get_sentence_ptr to allow acces to the senetnce shared_ptr that's already there anyway

libwccl/sentencecontext.h

@@ -37,6 +37,11 @@ public:
 		return *sentence_;
 	}
 
+	/// Underlying sentence shared pointer accesor
+	const boost::shared_ptr<Corpus2::Sentence>& get_sentence_ptr() const {
+		return sentence_;
+	}
+
 	/// Shorthand to get_sentence().size()
 	int size() const {
 		return sentence_->size();