pgsql: minor code cleanup - replace useless struct timezone argument to

Log Message:
-----------

minor code cleanup - replace useless struct timezone argument to
gettimeofday with NULL in a few places, making it consistent with
usage elsewhere.

Modified Files:
--------------
    pgsql/src/backend/postmaster:
        postmaster.c (r1.471 -> r1.472)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/postmaster/postmaster.c.diff?r1=1.471&r2=1.472)
    pgsql/src/backend/utils/adt:
        nabstime.c (r1.145 -> r1.146)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/nabstime.c.diff?r1=1.145&r2=1.146)
    pgsql/src/backend/utils/misc:
        pg_rusage.c (r1.2 -> r1.3)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/misc/pg_rusage.c.diff?r1=1.2&r2=1.3)