pgsql: Rework libpq threaded SIGPIPE handling to avoid interference with

Log Message:
-----------
Rework libpq threaded SIGPIPE handling to avoid interference with
calling applications. This is done by blocking sigpipe in the libpq
thread and using sigpending/sigwait to possibily discard any sigpipe we
generated.

Modified Files:
--------------
pgsql:
configure (r1.409 -> r1.410)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/configure.diff?r1=1.409&r2=1.410)
configure.in (r1.387 -> r1.388)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/configure.in.diff?r1=1.387&r2=1.388)
pgsql/doc/src/sgml:
libpq.sgml (r1.169 -> r1.170)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/libpq.sgml.diff?r1=1.169&r2=1.170)
pgsql/doc/src/sgml/ref:
copy.sgml (r1.60 -> r1.61)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/copy.sgml.diff?r1=1.60&r2=1.61)
pgsql/src/interfaces/libpq:
fe-connect.c (r1.290 -> r1.291)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-connect.c.diff?r1=1.290&r2=1.291)
fe-print.c (r1.55 -> r1.56)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-print.c.diff?r1=1.55&r2=1.56)
fe-secure.c (r1.57 -> r1.58)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/fe-secure.c.diff?r1=1.57&r2=1.58)
libpq-fe.h (r1.113 -> r1.114)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/libpq-fe.h.diff?r1=1.113&r2=1.114)
libpq-int.h (r1.96 -> r1.97)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/libpq/libpq-int.h.diff?r1=1.96&r2=1.97)