Enforce "en" lang in tests.

Some tests compare the result to english strings.

Do not test UnixCommandExecutor on Windows.

PharTest: explain why PHAR writing test are skipped.

InstallCommandTest: mock checkRequirements to allow the tests to run.

Run php_parallel_lint before all other tests.

Close #846

Tests/PHPCI/Plugin/Util/ExamplePluginConfig.php

@@ -1,4 +1,13 @@
 <?php
+
+/**
+ * PHPCI - Continuous Integration for PHP
+ *
+ * @copyright    Copyright 2015, Block 8 Limited.
+ * @license      https://github.com/Block8/PHPCI/blob/master/LICENSE.md
+ * @link         https://www.phptesting.org/
+ */
+
 return function (PHPCI\Plugin\Util\Factory $factory) {
     $factory->registerResource(
         // This function will be called when the resource is needed.
@@ -10,4 +19,4 @@ return function (PHPCI\Plugin\Util\Factory $factory) {
         "requiredArgument",
         null
     );
-};
+};