pgsql: Add amcheck extension to contrib.

Add amcheck extension to contrib.

This is the beginning of a collection of SQL-callable functions to
verify the integrity of data files. For now it only contains code to
verify B-Tree indexes.

This adds two SQL-callable functions, validating B-Tree consistency to
a varying degree. Check the, extensive, docs for details.

The goal is to later extend the coverage of the module to further
access methods, possibly including the heap. Once checks for
additional access methods exist, we'll likely add some "dispatch"
functions that cover multiple access methods.

Author: Peter Geoghegan, editorialized by Andres Freund
Reviewed-By: Andres Freund, Tomas Vondra, Thomas Munro,
Anastasia Lubennikova, Robert Haas, Amit Langote
Discussion: CAM3SWZQzLMhMwmBqjzK+pRKXrNUZ4w90wYMUWfkeV8mZ3Debvw(at)mail(dot)gmail(dot)com

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/3717dc149ecf44b8be95350a68605ba7299474fd

Modified Files
--------------
contrib/Makefile | 1 +
contrib/amcheck/Makefile | 21 +
contrib/amcheck/amcheck--1.0.sql | 24 +
contrib/amcheck/amcheck.control | 5 +
contrib/amcheck/expected/check.out | 1 +
contrib/amcheck/expected/check_btree.out | 90 +++
contrib/amcheck/sql/check.sql | 1 +
contrib/amcheck/sql/check_btree.sql | 59 ++
contrib/amcheck/verify_nbtree.c | 1249 ++++++++++++++++++++++++++++++
doc/src/sgml/amcheck.sgml | 273 +++++++
doc/src/sgml/contrib.sgml | 1 +
doc/src/sgml/filelist.sgml | 1 +
src/tools/pgindent/typedefs.list | 2 +
13 files changed, 1728 insertions(+)