[Dundi] DUNDi PRECACHE/PUSH stuff

[Mark Spencer]

So to explain the PRECACHE/PUSH, it's basically designed to allow you to 
use some TRIP-like functionality within the otherwise inverted TRIP 
architecture of DUNDi.  Essentially it allows you to push routes 
(typically up to another node).  In this way, servers which are on highly 
latent connections, or have only a few distinct routes, can simply push 
their few routes up to the next higher node and they will no longer have 
to be queried.  Essentially PRECACHE provides answers for questions that 
have not been asked.  You can enable precache inbound or outbound with 
"pcmodel=" on a system.  You may not have inbound for pcmodel and model, 
or outbound for both pcmodel and model, but Asterisk will warn you about 
those combos anyway.

It's pretty new, please feel free to play with it, still have to do 
patterns...

Mark