Group by expressions

Agenda for 2010-08-31:
 > Projecting expressions used for grouping - see recent discussion of 
ISSUE-41 on the mailing list

Input: The current grammar has:

[20]  GroupCondition  ::=
    ( BuiltInCall
    |  FunctionCall
    |  '(' Expression ( 'AS' Var )? ')'
    | Var )

and the name introduced can then be used in SELECT expressions and HAVING.

SELECT (?o3+128 AS ?o4)
{
....
}
GROUP BY (?o1+?o2 AS ?o3)
HAVING ( ?o3 > 45)

Currently, the name is optional, reflecting that it may not be used 
again if it's not mentioned in HAVING or SELECT.  This avoids needing to 
require sub-expression determination.

	Andy