namecache redesign

[tridge at samba.org]

> I'll just mention that the caching code in the ubiqx subdirectory is fully
> capable of handling all of this stuff.

ahh, no, not even close!

The cache needs to be persistent, and needs to be shared between
processes. It also needs to be able to be managed externally (I
proposed a 'net cache' interface). It should be pretty simple to
implement on top of tdb though.

The reason it needs to be persistant is that we will use gencache to
perform longer term caching of some information, for example the
mapping between the workgroup name and the realm name. Doing
persistant caching of NBT names will also be useful to cope with a
WINS server being down at startup.

Cheers, Tridge