pgsql: Remove justify_hours call from interval_mul and interval_div, and

Log Message:
-----------
Remove justify_hours call from interval_mul and interval_div, and make
some small stylistic improvements in these functions.  Also fix several
places where TMODULO() was being used with wrong-sized quotient argument,
creating a risk of overflow --- interval2tm was actually capable of going
into an infinite loop because of this.

Modified Files:
--------------
    pgsql/src/backend/utils/adt:
        timestamp.c (r1.155 -> r1.156)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/timestamp.c.diff?r1=1.155&r2=1.156)
    pgsql/src/test/regress/expected:
        interval.out (r1.13 -> r1.14)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/interval.out.diff?r1=1.13&r2=1.14)