Prepared queries notes

[Alan DeKok]

  I've put some notes about prepared queries on github:

https://github.com/FreeRADIUS/freeradius-server/issues/830

  In short, it seems to be relatively simple.  There's some magic in
turning:

	SELECT ... %{User-Name} ...

  into

	PREPARE fooplan (int, text, bool, numeric) AS
	    SELECT foo VALUES($1, $2, $3, $4);

  followed by:

	EXECUTE fooplan(1, 'Hunter Valley', 't', 200.00);

  But it doesn't seem impossible.

  Alan DeKok.