More log messages and less errors in the authentication via LDAP

The most important change was when creating a new user. The values passed need
to be ruby strings, but they were classes defined by net-ldap. This was causing
errors in the gem "valid_email", so now we make sure the values will always
be strings.
More details at: https://github.com/hallelujah/valid_email/issues/22

refs #246