When running XHPAST unit tests, include the "syntax error" lint rule

Summary:
See rARC3ffed59bd7. Currently, when a unit test includes a syntax error, it is raised in an unclear way ("error at line 10, char 1: XHP1 Unknown lint message!").

This is because each test case only activates rules it wants to test, so we lose the ID/name for the syntax message. However, we always want to test this and the lint engine can always raise it.

To get a better error message, include it unconditionally. So a test for rule `X` really tests two rules: syntax, and `X`.

Test Plan:
Ran `arc unit` at HEAD, got a better test failure:

```
   FAIL  ArcanistCallTimePassByReferenceXHPASTLinterRuleTestCase::testLinter
In 'call-time-pass-by-reference.lint-test', expected lint to raise error on line 10 at char 8, but no error was raised. Actually raised:
  error at line 10, char 1: XHP1 PHP Syntax Error!
```

NOTE: This doesn't pass tests yet, it just makes the test failure easier to understand. I'll see about fixing the test in the next change.

Reviewers: chad, richardvanvelzen

Reviewed By: richardvanvelzen

Differential Revision: https://secure.phabricator.com/D15819

src/lint/linter/xhpast/rules/__tests__/ArcanistXHPASTLinterRuleTestCase.php

@@ -8,8 +8,19 @@ abstract class ArcanistXHPASTLinterRuleTestCase
   extends ArcanistLinterTestCase {
 
   final protected function getLinter() {
+    // Always include this rule so we get good messages if a test includes
+    // a syntax error. No normal test should contain syntax errors.
+    $syntax_rule = new ArcanistSyntaxErrorXHPASTLinterRule();
+
+    $test_rule = $this->getLinterRule();
+
+    $rules = array(
+      $syntax_rule,
+      $test_rule,
+    );
+
     return id(new ArcanistXHPASTLinter())
-      ->setRules(array($this->getLinterRule()));
+      ->setRules($rules);
   }
 
   /**