[BUGFIX] EXT:rsaauth is not supported in TYPO3 < 4.7

Authentication does not work when RSA is used to encrypt passwords:

    $GLOBALS['TYPO3_CONF_VARS']['BE']['loginSecurityLevel'] = 'rsa';
    $GLOBALS['TYPO3_CONF_VARS']['FE']['loginSecurityLevel'] = 'rsa';

Prior to TYPO3 4.7, RSA was registered as a standard authentication
service and its priority is lower than LDAP. This leads to reading an
empty plain text password and therefor prevents the user to login.

Fixes: #61191
Change-Id: I4e9a094bcb36288bd6eb47fce423dc60082d9d94
Reviewed-on: http://review.typo3.org/32401
Reviewed-by: Thierry Brodard <thierry.brodard@techniconcept.ch>
Reviewed-by: Daniel Regelein <daniel.regelein@diehl-informatik.de>
Tested-by: Daniel Regelein <daniel.regelein@diehl-informatik.de>
Reviewed-by: Xavier Perseguers <xavier@typo3.org>
Tested-by: Xavier Perseguers <xavier@typo3.org>