pgsql: Exclude additional directories in pg_basebackup

Exclude additional directories in pg_basebackup

The list of files and directories that pg_basebackup excludes from the
backup was somewhat incomplete and unorganized.  Change that with having
the exclusion driven from tables.  Clean up some code around it.  Also
document the exclusions in more detail so that users of pg_start_backup
can make use of it as well.

The contents of these directories are now excluded from the backup:
pg_dynshmem, pg_notify, pg_serial, pg_snapshots, pg_subtrans

Also fix a bug that a pg_repl_slot or pg_stat_tmp being a symlink would
cause a corrupt tar header to be created.  Now such symlinks are
included in the backup as empty directories.  Bug found by Ashutosh
Sharma <ashu.coek88@gmail.com>.

From: David Steele <david@pgmasters.net>
Reviewed-by: Michael Paquier <michael.paquier@gmail.com>

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/6ad8ac6026287e3ccbc4d606b6ab6116ccc0eec8

Modified Files
--------------
doc/src/sgml/backup.sgml                     |  16 ++
doc/src/sgml/protocol.sgml                   |  13 +-
doc/src/sgml/ref/pg_basebackup.sgml          |  10 +-
src/backend/replication/basebackup.c         | 260 +++++++++++++++++----------
src/bin/pg_basebackup/t/010_pg_basebackup.pl |  44 ++++-
5 files changed, 243 insertions(+), 100 deletions(-)