pgsql: Use latch instead of select() in walreceiver

Use latch instead of select() in walreceiver

Replace use of poll()/select() by WaitLatchOrSocket(), which is more
portable and flexible.

Also change walreceiver to use its procLatch instead of a custom latch.

From: Petr Jelinek <petr(at)2ndquadrant(dot)com>

Branch
------
master

Details
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http://git.postgresql.org/pg/commitdiff/597a87ccc9a6fa8af7f3cf280b1e24e41807d555

Modified Files
--------------
src/backend/postmaster/pgstat.c | 3 +
.../libpqwalreceiver/libpqwalreceiver.c | 101 +++++----------------
src/backend/replication/walreceiver.c | 18 ++--
src/backend/replication/walreceiverfuncs.c | 6 +-
src/include/pgstat.h | 1 +
src/include/replication/walreceiver.h | 3 +-
6 files changed, 43 insertions(+), 89 deletions(-)