Add quit command

Change-Id: Ia0a01a558ec92bb0d8f22fe2fbddf74b8d78242b
diff --git a/src/interpreter.cpp b/src/interpreter.cpp
index 0fe96da..d139e8b 100644
--- a/src/interpreter.cpp
+++ b/src/interpreter.cpp
@@ -291,6 +291,11 @@
     }
 }
 
+void Interpreter::operator()(const quit_&) const
+{
+    // no operation
+}
+
 template <typename PathType>
 boost::variant<dataPath_, schemaPath_, module_> Interpreter::toCanonicalPath(const boost::optional<PathType>& optPath) const
 {