Add check for dom extension (bug 3362)

Signed-off-by: Richard Mansfield <richardm@catalyst.net.nz>

htdocs/lang/en.utf8/error.php

@@ -33,6 +33,7 @@ $string['jsonextensionnotloaded'] = 'Your server configuration does not include
 $string['pgsqldbextensionnotloaded'] = 'Your server configuration does not include the pgsql extension. Mahara requires this in order to store data in a relational database. Please make sure that it is loaded in php.ini, or install it if it is not installed.';
 $string['mysqldbextensionnotloaded'] = 'Your server configuration does not include the mysql extension. Mahara requires this in order to store data in a relational database. Please make sure that it is loaded in php.ini, or install it if it is not installed.';
 $string['unknowndbtype'] = 'Your server configuration references an unknown database type. Valid values are "postgres8" and "mysql5". Please change the database type setting in config.php.';
+$string['domextensionnotloaded'] = 'Your server configuration does not include the dom extension. Mahara requires this in order to parse XML data from a variety of sources.';
 $string['xmlextensionnotloaded'] = 'Your server configuration does not include the %s extension. Mahara requires this in order to parse XML data from a variety of sources. Please make sure that it is loaded in php.ini, or install it if it is not installed.';
 $string['gdextensionnotloaded'] = 'Your server configuration does not include the gd extension. Mahara requires this in order to perform resizes and other operations on uploaded images. Please make sure that it is loaded in php.ini, or install it if it is not installed.';
 $string['gdfreetypenotloaded'] = 'Your server configuration of the gd extension does not include Freetype support. Mahara requires this to in order to build CAPTCHA images. Please make sure that gd is configured with it.';

htdocs/lib/mahara.php

@@ -73,6 +73,9 @@ function ensure_sanity() {
     if(!extension_loaded('curl')) {
         throw new ConfigSanityException(get_string('curllibrarynotinstalled', 'error'));
     }
+    if (!extension_loaded('dom')) {
+        throw new ConfigSanityException(get_string('domextensionnotloaded', 'error'));
+    }
 
     //Check for freetype in the gd extension
     $gd_info = gd_info();