[krbdev.mit.edu #2153] MSLSA ccache should not output TGTs with NULL session keys

[Jeffrey Altman via RT]

The Windows Kerberos LSA will by default on the next generation of
service packs not export session keys for TGTs, only service tickets. 
In this circumstance, the MSLSA ccache should not output the ticket if
there is a NULL enctype set.