"set sources" and data cacheing

[Nick Hilliard]

Looks like the "@rtconfig set sources" command does not interact properly
with the object cache:

> rtconfig> @rtconfig set sources = "RIPE"
> rtconfig> @rtconfig printPrefixes "can haz %p/%l\n" filter as-inexie
> can haz 193.242.111.0/24
> can haz 194.88.240.0/23
> rtconfig> @rtconfig set sources = "RADB"
> rtconfig> @rtconfig printPrefixes "can haz %p/%l\n" filter as-inexie
> can haz 193.242.111.0/24
> can haz 194.88.240.0/23
> rtconfig> 

The second command should return nothing because there is no data in
whois.radb.net keyed on AS-INEXIE with source "RADB".

I haven't really looked at the cacheing code.  Does the code store the
object source: tag?  If it does, this is should be a relatively simple bug.
 If it doesn't, then there's a choice between getting the cache to store
the source: tag and making that work correctly, or alternatively any time
someone changes the source list, then the entire cache could be
invalidated.  The latter is obviously pretty icky.

Nick