/*
 * call-seq:
 *    Sys::Admin.get_login
 *
 * Returns the login for the process. If this is called from a process that
 * has no controlling terminal, then it resorts to returning the "LOGNAME" or
 * "USER" environment variable.  If neither of those is defined, then nil
 * is returned.
 *
 * Note that this method will _probably_ return the real user login, but may
 * return the effective user login. YMMV depending on your platform and how
 * the program is run.
 */
static VALUE admin_get_login(VALUE klass){