new rlm_sql connection pool logic

[Alan DeKok]

Arran Cudbard-Bell wrote:
>> The next thing is to limit the number of connections to one if there
>> are no threads.  It makes no sense to open a dozen connections when the
>> server is running in debugging mode.
> 
> Well, you know, except for debugging ? 

$ radiusd -xxx ...

  Debugging, with threads.

$ radiusd -X ...

  Debugging, without threads.

  Does it make sense to open 5 DB connections when there's only one thread?

  Alan DeKok.