Extensions (such as the hieroglyphic module WikiHiero) are distributed
separately. Drop them into this extensions directory and enable as
per the extension's directions.

If you are a developer, you want to fetch the extension tree in another
directory and make a symbolic link:

 mediawiki/extensions$ ln -s ../../extensions-trunk/FooBarExt

The extensions are available through svn at:
    http://svn.wikimedia.org/svnroot/mediawiki/trunk/extensions/

You can find documentation and additional extensions on MediaWiki website:
    http://www.mediawiki.org/wiki/Category:Extensions


Please note that under POSIX systems (Linux...), parent of a symbolic path
refers to the link source, NOT to the target! You should check the env
variable MW_INSTALL_PATH in case the extension is not in the default location.

The following code snippet let you override the default path: 

 $IP = getenv( 'MW_INSTALL_PATH' );
 if( $IP === false ) {
	$IP = dirname( __FILE__ ) . '/../..';
 }
 require( "$IP/maintenance/Maintenance.php" ); // a MediaWiki core file