[SSSD] [PATCH] Serialize requests of the same user in the krb5 provider

[Sumit Bose]

Hi,

I would like to propose this patch as an alternative fix for ticket
#533. This patch puts parallel auth requests of a user in a wait queue
and handles them one after the other. This will delay parallel auth
requests a bit but avoids all kind of race conditions I still can see in
the approach for creating the potential new ccache file at the beginning
of the request.

bye,
Sumit