pgsql: Don't generate parallel paths for rels with parallel-restricted

Don't generate parallel paths for rels with parallel-restricted outputs.

Such paths are unsafe.  To make it cheaper to detect when this case
applies, track whether a relation's default PathTarget contains any
non-Vars.  In most cases, the answer will be no, which enables us to
determine cheaply that the target list for a proposed path is
parallel-safe.  However, subquery pull-up can create cases that
require us to inspect the target list more carefully.

Amit Kapila, reviewed by me.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/b12fd41c695b43c76b0a9a4d19ba43b05536440c

Modified Files
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src/backend/nodes/outfuncs.c             |  1 +
src/backend/optimizer/path/allpaths.c    | 10 ++++++++++
src/backend/optimizer/util/placeholder.c |  2 ++
src/backend/optimizer/util/relnode.c     | 10 +++++++---
src/include/nodes/relation.h             |  2 ++
5 files changed, 22 insertions(+), 3 deletions(-)