Use PMA_MAJOR_VERSION as a constant

Looking at bootstrap-dist.php, it looks like PMA_MAJOR_VERSION was in fact intended to be used as a constant

Signed-off-by: Madhura Jayaratne <madhura.cj@gmail.com>

libraries/Config.php

@@ -1456,6 +1456,7 @@ class Config
 
         $defines = array(
             'PMA_VERSION',
+            'PMA_MAJOR_VERSION',
             'PMA_THEME_VERSION',
             'PMA_THEME_GENERATION',
             'PMA_IS_WINDOWS',

libraries/Theme.php

@@ -118,7 +118,7 @@ class Theme
         if (! is_array($data['supports'])) {
             return false;
         }
-        if (! in_array($GLOBALS['PMA_Config']->get('PMA_MAJOR_VERSION'), $data['supports'])) {
+        if (! in_array(PMA_MAJOR_VERSION, $data['supports'])) {
             return false;
         }