pgsql: Add quotes around search_path "$user" so that SHOW output can be

Log Message:
-----------
Add quotes around search_path "$user" so that SHOW output can be used in
SET.

Modified Files:
--------------
pgsql/doc/src/sgml:
config.sgml (r1.39 -> r1.40)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml.diff?r1=1.39&r2=1.40)
ddl.sgml (r1.50 -> r1.51)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ddl.sgml.diff?r1=1.50&r2=1.51)
pgsql/src/backend/utils/misc:
guc.c (r1.302 -> r1.303)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c.diff?r1=1.302&r2=1.303)
postgresql.conf.sample (r1.171 -> r1.172)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/postgresql.conf.sample.diff?r1=1.171&r2=1.172)