pgsql: Add stats for min, max, mean, stddev times to pg_stat_statements

Add stats for min, max, mean, stddev times to pg_stat_statements.

The new fields are min_time, max_time, mean_time and stddev_time.

Based on an original patch from Mitsumasa KONDO, modified by me. Reviewed by Petr Jelínek.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/717f709532642f5f7756785c9be17b7ffcec8ae8

Modified Files
--------------
contrib/pg_stat_statements/Makefile                |    5 +-
.../pg_stat_statements--1.2--1.3.sql               |   47 +++++++++++
.../pg_stat_statements/pg_stat_statements--1.2.sql |   44 ----------
.../pg_stat_statements/pg_stat_statements--1.3.sql |   48 +++++++++++
contrib/pg_stat_statements/pg_stat_statements.c    |   87 +++++++++++++++++++-
.../pg_stat_statements/pg_stat_statements.control  |    2 +-
doc/src/sgml/pgstatstatements.sgml                 |   28 +++++++
7 files changed, 212 insertions(+), 49 deletions(-)