Renamed yii.php -> Yii.php for class, filename consitency

See yiisoft#123 (comment)
Issue yiisoft#123

apps/bootstrap/index.php

@@ -3,7 +3,7 @@
 defined('YII_DEBUG') or define('YII_DEBUG', true);
 
 $frameworkPath = __DIR__ . '/../../framework/';
-require($frameworkPath . 'yii.php');
+require($frameworkPath . 'Yii.php');
 
 $config = require(__DIR__ . '/protected/config/main.php');
 $application = new yii\web\Application($config);

build/build

@@ -11,7 +11,7 @@
 // fcgi doesn't have STDIN defined by default
 defined('STDIN') or define('STDIN', fopen('php://stdin', 'r'));
 
-require(__DIR__ . '/../framework/yii.php');
+require(__DIR__ . '/../framework/Yii.php');
 
 $id = 'yiic-build';
 $basePath = __DIR__;

framework/yiic.php

@@ -12,7 +12,7 @@
 // fcgi doesn't have STDIN defined by default
 defined('STDIN') or define('STDIN', fopen('php://stdin', 'r'));
 
-require(__DIR__ . '/yii.php');
+require(__DIR__ . '/Yii.php');
 
 $application = new yii\console\Application(array(
 	'id' => 'yiic',

tests/unit/bootstrap.php

@@ -5,7 +5,7 @@
 $_SERVER['SCRIPT_NAME'] = '/' . __DIR__;
 $_SERVER['SCRIPT_FILENAME'] = __FILE__;
 
-require_once(__DIR__ . '/../../framework/yii.php');
+require_once(__DIR__ . '/../../framework/Yii.php');
 
 Yii::setAlias('@yiiunit', __DIR__);
 

tests/web/app/index.php

@@ -1,6 +1,6 @@
 <?php
 
-require(__DIR__ . '/../../../framework/yii.php');
+require(__DIR__ . '/../../../framework/Yii.php');
 
 $application = new yii\web\Application('test', __DIR__ . '/protected');
 $application->run();