pgsql: Back-patch assorted latch-related fixes.

Back-patch assorted latch-related fixes.

Fix a whole bunch of signal handlers that had been hacked to do things that
might change errno, without adding the necessary save/restore logic for
errno.  Also make some minor fixes in unix_latch.c, and clean up bizarre
and unsafe scheme for disowning the process's latch.  While at it, rename
the PGPROC latch field to procLatch for consistency with 9.2.

Issues noted while reviewing a patch by Peter Geoghegan.

Branch
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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/989f530d3f793ed1c990d705d0958bfd2a533b85

Modified Files
--------------
src/backend/access/transam/xlog.c     |   16 +++++++++++
src/backend/port/unix_latch.c         |   47 ++++++++++++++++++++++++++++-----
src/backend/replication/syncrep.c     |   17 +++--------
src/backend/replication/walreceiver.c |    4 +++
src/backend/replication/walsender.c   |   16 +++++++++++
src/backend/storage/lmgr/proc.c       |   42 +++++++++++++++++++++-------
src/backend/tcop/postgres.c           |   14 +++++----
src/include/replication/syncrep.h     |    4 +-
src/include/storage/proc.h            |    3 +-
9 files changed, 124 insertions(+), 39 deletions(-)