ClearAll does not clear Qualifiers

[DelcioSbeghen]

ClearAll and Select.Clear does not clear qualifiers(First, Skip, Distinct).

Proposed change in GpSQLBuilder.AST.pas:

procedure TGpSQLSelect.Clear;
begin
  Columns.Clear;
  TableNames.Clear;
end;

to

procedure TGpSQLSelect.Clear;
begin
  Columns.Clear;
  TableNames.Clear;
  Qualifiers.Clear;
end;