Log Message:
-----------
Fix define_custom_variable to preserve any sourcefile/sourceline information
present in the placeholder. Noted while testing pg_stat_statements.
Modified Files:
--------------
pgsql/src/backend/utils/misc:
guc.c (r1.488 -> r1.489)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c?r1=1.488&r2=1.489)