pgsql: Expose qurey ID in pg_stat_statements view.

Expose qurey ID in pg_stat_statements view.

The query ID is the internal hash identifier of the statement,
and was not available in pg_stat_statements view so far.

Daniel Farina, Sameer Thakur and Peter Geoghegan, reviewed by me.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/91484409bdd17f330d10671d388b72d4ef1451d7

Modified Files
--------------
contrib/pg_stat_statements/Makefile                |    4 +-
.../pg_stat_statements--1.1--1.2.sql               |   43 +++++++++++
.../pg_stat_statements/pg_stat_statements--1.1.sql |   43 -----------
.../pg_stat_statements/pg_stat_statements--1.2.sql |   44 ++++++++++++
contrib/pg_stat_statements/pg_stat_statements.c    |   62 +++++++++++++---
.../pg_stat_statements/pg_stat_statements.control  |    2 +-
doc/src/sgml/pgstatstatements.sgml                 |   75 ++++++++++++++++----
7 files changed, 202 insertions(+), 71 deletions(-)