pgsql: Support having multiple Unix-domain sockets per postmaster.

Support having multiple Unix-domain sockets per postmaster.

Replace unix_socket_directory with unix_socket_directories, which is a list
of socket directories, and adjust postmaster's code to allow zero or more
Unix-domain sockets to be created.

This is mostly a straightforward change, but since the Unix sockets ought
to be created after the TCP/IP sockets for safety reasons (better chance
of detecting a port number conflict), AddToDataDirLockFile needs to be
fixed to support out-of-order updates of data directory lockfile lines.
That's a change that had been foreseen to be necessary someday anyway.

Honza Horak, reviewed and revised by Tom Lane

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/c9b0cbe98bd783e24a8c4d8d8ac472a494b81292

Modified Files
--------------
doc/src/sgml/client-auth.sgml | 2 +-
doc/src/sgml/config.sgml | 35 +++++---
doc/src/sgml/ref/postgres-ref.sgml | 10 ++-
doc/src/sgml/runtime.sgml | 2 +-
src/backend/libpq/pqcomm.c | 92 +++++++++++++-------
src/backend/postmaster/postmaster.c | 75 ++++++++++++----
src/backend/tcop/postgres.c | 2 +-
src/backend/utils/adt/varlena.c | 110 ++++++++++++++++++++++
src/backend/utils/init/miscinit.c | 120 +++++++++++++++---------
src/backend/utils/misc/guc.c | 12 ++-
src/backend/utils/misc/postgresql.conf.sample | 3 +-
src/bin/initdb/initdb.c | 11 ++-
src/bin/pg_ctl/pg_ctl.c | 2 +-
src/include/libpq/libpq.h | 8 +-
src/include/miscadmin.h | 7 +-
src/include/postmaster/postmaster.h | 2 +-
src/include/utils/builtins.h | 2 +
17 files changed, 369 insertions(+), 126 deletions(-)