Adding support for getting a new config file from the same directory as the...

Adding support for getting a new config file from the same directory as the current one. Used in example in the login modules that hae their own cofig file in addition to config.php.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@492 44740490-163a-0410-bde0-09ae8108e29a