Add 'group by ... keeping ...' as a synonym of 'group by ... with ...'.

Change-Id: I9aa7354092e13d7a95a3ab0ee4b02a468dbf3baf
Reviewed-on: http://fulliautomatix.ics.uci.edu:8443/187
Tested-by: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Reviewed-by: Till Westmann <westmann@gmail.com>
28 files changed