pgsql: Extend amcheck to check heap pages.

Extend amcheck to check heap pages.

Mark Dilger, reviewed by Peter Geoghegan, Andres Freund, Álvaro Herrera,
Michael Paquier, Amul Sul, and by me. Some last-minute cosmetic
revisions by me.

Discussion: http://postgr.es/m/12ED3DA8-25F0-4B68-937D-D907CFBF08E7@enterprisedb.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/866e24d47db1743dfcff5bd595b57e3a143f2cb1

Modified Files
--------------
contrib/amcheck/Makefile                |    7 +-
contrib/amcheck/amcheck--1.2--1.3.sql   |   30 +
contrib/amcheck/amcheck.control         |    2 +-
contrib/amcheck/expected/check_heap.out |  194 +++++
contrib/amcheck/sql/check_heap.sql      |  116 +++
contrib/amcheck/t/001_verify_heapam.pl  |  242 ++++++
contrib/amcheck/verify_heapam.c         | 1447 +++++++++++++++++++++++++++++++
doc/src/sgml/amcheck.sgml               |  235 ++++-
src/backend/access/heap/hio.c           |   11 +
src/backend/access/transam/multixact.c  |   19 +
src/include/access/multixact.h          |    1 +
src/tools/pgindent/typedefs.list        |    4 +
12 files changed, 2299 insertions(+), 9 deletions(-)