User::getGroupID loose value check

User::getGroupID() may return NULL or "0" depending whether user had groups set earlier and so on
fix accidental lowercase from 6f6a0b2d
update copyright year
store ldap configuration in plain php file

base64 obfuscation is not worth of it, var_export exists since php 4.2.0
old base64 encoded format is still readed, but not written