pgsql: Change the default value of standard_conforming_strings to on.

Log Message:
-----------
Change the default value of standard_conforming_strings to on.

This change should be publicized to driver maintainers at once and
release-noted as an incompatibility with previous releases.

Modified Files:
--------------
pgsql/doc/src/sgml:
config.sgml (r1.296 -> r1.297)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml?r1=1.296&r2=1.297)
syntax.sgml (r1.147 -> r1.148)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/syntax.sgml?r1=1.147&r2=1.148)
pgsql/src/backend/parser:
scan.l (r1.167 -> r1.168)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/scan.l?r1=1.167&r2=1.168)
pgsql/src/backend/utils/misc:
guc.c (r1.562 -> r1.563)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c?r1=1.562&r2=1.563)
postgresql.conf.sample (r1.291 -> r1.292)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/postgresql.conf.sample?r1=1.291&r2=1.292)