Re: WIP Patch for GROUPING SETS phase 1

The following review has been posted through the commitfest application:
make installcheck-world:  tested, failed
Implements feature:       tested, passed
Spec compliant:           not tested
Documentation:            tested, passed

This is a midway review, a later will complete it. 

The patch applies against 8d1f239003d0245dda636dfa6cf0add13bee69d6 and builds correctly. Make installcheck-world fails,
butit seems to be somewhere totally unrelated (TCL pl)... 
 

The documentation is very well-written and the patch implements the documented syntax.

I still need to check against the standard and I will run it against a non-trivival production load... hopefully I will
finishup my review shortly after the weekend...