s4:pwsettings: Added validation.

s4:pwsettings: Added validation.

Validate that each field is within its allowed range.  Also validate that the
maximum password age is greater than the minimum password length (if the maximum
password age is set).

I could not find these values documented anywhere in the WSPP docs.  I used the
values shown in the W2K8 GPMC, as it appears that the GPMC actuaally performs
the validation of values.