pgsql: Re-apply guc cleanup patch, with memory allocation bugs fixed.

Log Message:
-----------
Re-apply guc cleanup patch, with memory allocation bugs fixed.

Modified Files:
--------------
pgsql/src/backend/utils/misc:
guc-file.l (r1.42 -> r1.43)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc-file.l.diff?r1=1.42&r2=1.43)
guc.c (r1.337 -> r1.338)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/guc.c.diff?r1=1.337&r2=1.338)
pgsql/src/include/utils:
guc.h (r1.73 -> r1.74)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/guc.h.diff?r1=1.73&r2=1.74)