completely new winbindd cache infrastructure

completely new winbindd cache infrastructure

this one looks like just another winbind backend, and has the
following properties:

- does -ve and +ve cacheing of all queries

- can be disabled with -n switch to winbindd

- stores all records packed, so even huge domains are not a problem
for a complete cache

- handles the server being down

- uses sequence numbers for all entries

This fixes a lot of problems with winbindd. Serving from cache is now
*very* fast.
(This used to be commit fddb4f4c04473a60a97212c0c8e143d6a4d68380)