pgsql: Add ALTER SYSTEM command to edit the server configuration file.

Add ALTER SYSTEM command to edit the server configuration file.

Patch contributed by Amit Kapila. Reviewed by Hari Babu, Masao Fujii,
Boszormenyi Zoltan, Andres Freund, Greg Smith and others.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/65d6e4cb5c62371dae6c236a7e709d503ae6ddf8

Modified Files
--------------
doc/src/sgml/config.sgml             |   13 +
doc/src/sgml/ref/allfiles.sgml       |    1 +
doc/src/sgml/ref/alter_system.sgml   |  114 +++++++
doc/src/sgml/reference.sgml          |    1 +
doc/src/sgml/storage.sgml            |    6 +
src/backend/nodes/copyfuncs.c        |   13 +
src/backend/nodes/equalfuncs.c       |   12 +
src/backend/parser/gram.y            |   27 +-
src/backend/replication/basebackup.c |    7 +
src/backend/tcop/utility.c           |   13 +
src/backend/utils/misc/guc-file.l    |   35 +-
src/backend/utils/misc/guc.c         |  614 +++++++++++++++++++++++++++++-----
src/bin/initdb/initdb.c              |   16 +
src/include/nodes/nodes.h            |    1 +
src/include/nodes/parsenodes.h       |   10 +
src/include/pg_config_manual.h       |    7 +
src/include/storage/lwlock.h         |    1 +
src/include/utils/guc.h              |    1 +
18 files changed, 797 insertions(+), 95 deletions(-)