Simul efun: query_variable - fetch the value of an element of an alist

Synopsis:
	mixed query_variable(mixed* pool, string variable)

Description:
	Returns the contents associated to key 'variable' from the
	varpool 'pool', or 0 if it can't be found.

Note:
	Kiri says: "I don't trust those simulated efuns and real efuns
	messing with alists! 'assoc' is not clean - at least not clean
	as simple replacement for 'member_array'!"

See also: lib/set_variable, efun/order_alist, efun/assoc, LPC/alists