Fix a minor i18n issue in libphutil

Summary:
Ref T5267. Fixes a missing `%s`.

Also ignores the `src/.cache/` directory, used for the i18n cache.

Test Plan: Extracted strings more cleanly.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T5267

Differential Revision: https://secure.phabricator.com/D16809

.gitignore

@@ -26,6 +26,7 @@
 
 # libphutil
 /src/.phutil_module_cache
+/src/.cache
 /support/phutiltestlib/.phutil_module_cache
 
 # This file overrides "default.pem" if present.

src/aphront/writeguard/AphrontWriteGuard.php

@@ -98,7 +98,7 @@ public function dispose() {
     if ($this->allowDepth > 0) {
       throw new Exception(
         pht(
-          'Imbalanced %s: more % calls than %s calls.',
+          'Imbalanced %s: more %s calls than %s calls.',
           __CLASS__,
           'beginUnguardedWrites()',
           'endUnguardedWrites()'));