pgsql: Fix EXPLAIN VERBOSE output for parallel aggregate.

Fix EXPLAIN VERBOSE output for parallel aggregate.

The way that PartialAggregate and FinalizeAggregate plan nodes were
displaying output columns before was bogus. Now, FinalizeAggregate
produces the same outputs as an Aggregate would have produced, while
PartialAggregate produces each of those outputs prefixed by the word
PARTIAL.

Discussion: 12585(dot)1460737650(at)sss(dot)pgh(dot)pa(dot)us

Patch by me, reviewed by David Rowley.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/59eb55127906b943ff155240eebc161df8edb62f

Modified Files
--------------
src/backend/nodes/copyfuncs.c | 2 +
src/backend/nodes/equalfuncs.c | 2 +
src/backend/nodes/outfuncs.c | 2 +
src/backend/nodes/readfuncs.c | 2 +
src/backend/optimizer/plan/setrefs.c | 5 +
src/backend/optimizer/util/tlist.c | 3 +
src/backend/utils/adt/ruleutils.c | 228 +++++++++++++++++++++++------------
src/include/nodes/primnodes.h | 2 +
8 files changed, 168 insertions(+), 78 deletions(-)