pgsql: Eliminate "parallel degree" terminology.

Eliminate "parallel degree" terminology.

This terminology provoked widespread complaints. So, instead, rename
the GUC max_parallel_degree to max_parallel_workers_per_gather
(leaving room for a possible future GUC max_parallel_workers that acts
as a system-wide limit), and rename the parallel_degree reloption to
parallel_workers. Rename structure members to match.

These changes create a dump/restore hazard for users of PostgreSQL
9.6beta1 who have set the reloption (or applied the GUC using ALTER
USER or ALTER DATABASE).

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/c9ce4a1c61ebf39c03885cc19fe7c32edc04a300

Modified Files
--------------
doc/src/sgml/config.sgml | 10 ++--
doc/src/sgml/ref/create_table.sgml | 12 ++--
doc/src/sgml/release-9.6.sgml | 2 +-
src/backend/access/common/reloptions.c | 6 +-
src/backend/nodes/outfuncs.c | 2 +-
src/backend/optimizer/path/allpaths.c | 34 +++++------
src/backend/optimizer/path/costsize.c | 8 +--
src/backend/optimizer/plan/createplan.c | 2 +-
src/backend/optimizer/plan/planner.c | 6 +-
src/backend/optimizer/util/pathnode.c | 86 +++++++++++++--------------
src/backend/optimizer/util/plancat.c | 4 +-
src/backend/optimizer/util/relnode.c | 2 +-
src/backend/utils/misc/guc.c | 4 +-
src/backend/utils/misc/postgresql.conf.sample | 2 +-
src/bin/psql/tab-complete.c | 2 +-
src/include/nodes/relation.h | 4 +-
src/include/optimizer/cost.h | 2 +-
src/include/optimizer/pathnode.h | 4 +-
src/include/utils/rel.h | 6 +-
19 files changed, 99 insertions(+), 99 deletions(-)