pgsql: Back out patch that allowed commented guc variables to return to

Log Message:
-----------
Back out patch that allowed commented guc variables to return to their
default values. Was causing regression failures.

Modified Files:
--------------
pgsql/src/backend/utils/misc:
guc-file.l (r1.40 -> r1.41)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc-file.l.diff?r1=1.40&r2=1.41)
guc.c (r1.335 -> r1.336)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c.diff?r1=1.335&r2=1.336)
pgsql/src/include/utils:
guc_tables.h (r1.25 -> r1.26)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/guc_tables.h.diff?r1=1.25&r2=1.26)