pgsql: pg_visibility: Add pg_truncate_visibility_map function.

pg_visibility: Add pg_truncate_visibility_map function.

This requires some core changes as well so that we can properly
WAL-log the truncation. Specifically, it changes the format of the
XLOG_SMGR_TRUNCATE WAL record, so bump XLOG_PAGE_MAGIC.

Patch by me, reviewed but not fully endorsed by Andres Freund.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/71d05a2c7b82379bb1013a0e338906349c54ed85

Modified Files
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contrib/pg_visibility/pg_visibility--1.0--1.1.sql | 7 +++
contrib/pg_visibility/pg_visibility--1.1.sql | 8 +++
contrib/pg_visibility/pg_visibility.c | 72 +++++++++++++++++++++++
doc/src/sgml/pgvisibility.sgml | 30 ++++++++--
src/backend/access/rmgrdesc/smgrdesc.c | 3 +-
src/backend/catalog/storage.c | 16 +++--
src/include/access/xlog_internal.h | 2 +-
src/include/catalog/storage_xlog.h | 8 +++
8 files changed, 133 insertions(+), 13 deletions(-)