pgsql: Create a psql command \gset to store query results into psql var

Create a psql command \gset to store query results into psql variables.

This eases manipulation of query results in psql scripts.

Pavel Stehule, reviewed by Piyush Newe, Shigeru Hanada, and Tom Lane

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/d2d153fdb08053d655bd0fef14187eed6a674193

Modified Files
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doc/src/sgml/ref/psql-ref.sgml | 40 ++++++++++++++
src/bin/psql/command.c | 18 ++++++-
src/bin/psql/common.c | 105 ++++++++++++++++++++++++++++++++---
src/bin/psql/help.c | 5 +-
src/bin/psql/settings.h | 1 +
src/bin/psql/tab-complete.c | 2 +-
src/test/regress/expected/psql.out | 54 ++++++++++++++++++
src/test/regress/parallel_schedule | 2 +-
src/test/regress/serial_schedule | 3 +-
src/test/regress/sql/psql.sql | 39 +++++++++++++
10 files changed, 254 insertions(+), 15 deletions(-)