GH-67 Optimized 'Having' and Grouping clause support
- Utilizes ECL HAVING function as recommended by Gavin.
- SQLFragment.getValue() incorporates special translation for fragments
of a Having clause in which the ECL 'ROWS' syntax is generated.
- Grouping clauses without having clauses are still processed as part of the
final result TABLE call for performance reasons.
- In ECLEngine, select structure is now based on the latest DS name.
- SQLParser found to be upcasing group by clause, thereby creating issues
in group by having clauses




Signed-off-by: Rodrigo Pastrana <Rodrigo.Pastrana@lexisnexis.com>
GH-67 changes from code review
pre-unary type fragments should have operand assigned to postfix.
Ensure function field is not null before making references to its methods.
Signed-off-by: Rodrigo Pastrana <Rodrigo.Pastrana@lexisnexis.com>
Merge pull request #78 from rpastrana/gh-67-havingjoinsupport

Gh 67 havingjoinsupport