pgsql: Code review for standard_conforming_strings patch.

Log Message:
-----------
Code review for standard_conforming_strings patch. Fix it so it does not
throw warnings for 100%-SQL-standard constructs, clean up some minor
infelicities, try to un-break ecpg to the best of my ability. (It's not clear
how ecpg is going to find out the setting of standard_conforming_strings,
though.) I think pg_dump still needs work, too.

Modified Files:
--------------
pgsql/doc/src/sgml:
config.sgml (r1.57 -> r1.58)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml.diff?r1=1.57&r2=1.58)
pgsql/src/backend/parser:
scan.l (r1.133 -> r1.134)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/parser/scan.l.diff?r1=1.133&r2=1.134)
pgsql/src/backend/utils/misc:
guc.c (r1.318 -> r1.319)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c.diff?r1=1.318&r2=1.319)
postgresql.conf.sample (r1.175 -> r1.176)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/postgresql.conf.sample.diff?r1=1.175&r2=1.176)
pgsql/src/bin/psql:
common.c (r1.116 -> r1.117)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/common.c.diff?r1=1.116&r2=1.117)
psqlscan.l (r1.17 -> r1.18)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/psqlscan.l.diff?r1=1.17&r2=1.18)
pgsql/src/include/parser:
gramparse.h (r1.34 -> r1.35)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/parser/gramparse.h.diff?r1=1.34&r2=1.35)
pgsql/src/include/utils:
guc.h (r1.67 -> r1.68)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/guc.h.diff?r1=1.67&r2=1.68)
pgsql/src/interfaces/ecpg/preproc:
pgc.l (r1.145 -> r1.146)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/preproc/pgc.l.diff?r1=1.145&r2=1.146)
pgsql/src/test/regress/expected:
strings.out (r1.28 -> r1.29)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/strings.out.diff?r1=1.28&r2=1.29)