Add throw.

tests/throw.rs

@@ -0,0 +1,18 @@
+use rhai::{Engine, EvalAltResult};
+
+#[test]
+fn test_throw() {
+    let mut engine = Engine::new();
+
+    match engine.eval::<i64>(r#"if true { throw "hello" }"#) {
+        Ok(_) => panic!("not an error"),
+        Err(EvalAltResult::ErrorRuntime(s, _)) if s == "hello" => (),
+        Err(err) => panic!("wrong error: {}", err),
+    }
+
+    match engine.eval::<i64>(r#"throw;"#) {
+        Ok(_) => panic!("not an error"),
+        Err(EvalAltResult::ErrorRuntime(s, _)) if s == "" => (),
+        Err(err) => panic!("wrong error: {}", err),
+    }
+}