Bug 11577: Expand description of AllowRenewalLimitOverride

Bug 11577: Expand description of AllowRenewalLimitOverride

With the introduction of the new automatic renewal feature global syspref
AllowRenewalLimitOverride is expanded in meaning. It now gives the option
to override blocks if:

- the number of allowed renewals is exceeded
- the renewal is premature (No renewal before)
- the item is scheduled for automatic renewal
- the renewal is premature and the item is scheduled for automatic renewal

Sponsored-by: Hochschule für Gesundheit (hsg), Germany
Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>