Improve keyword parsing, including for (#747)

* Improve keyword parsing, including for

* touchup

src/tests/test_engine.rs

@@ -143,3 +143,8 @@ fn proper_variable_captures_with_nesting() -> TestResult {
         "102",
     )
 }
+
+#[test]
+fn proper_variable_for() -> TestResult {
+    run_test(r#"for x in 1..3 { if $x == 2 { "bob" } } | get 1"#, "bob")
+}

src/tests/test_parser.rs

@@ -116,7 +116,7 @@ fn long_flag() -> TestResult {
 
 #[test]
 fn let_not_statement() -> TestResult {
-    fail_test(r#"let x = "hello" | str length"#, "can't")
+    fail_test(r#"let x = "hello" | str length"#, "used in pipeline")
 }
 
 #[test]