[krbdev.mit.edu #5477] Enable Vista support for MSLSA

[Kevin Koch via RT]

>... As of this commit, the functionality will be enabled if
>    the version of NTSecAPI.h includes
>    TRUST_ATTRIBUTE_TRUST_USES_AES_KEYS.  This is a preprocessor symbol
>    that is new to the Vista SDK.
> 
> In order to build with the new Vista functionality when using the XP
>    SP2 SDK, the NTSecAPI.h file from the Vista SDK must be used in
>    place of the version from the XP SP2 SDK.

The #define of TRUST_ATTRIBUTE_TRUST_USES_AES_KEYS is bracketted in #if 
(_WIN32_WINNT >= 0x0600).  How will the functionality be enabled if the 
product is built on XP?