pgsql: Fix interval input parser so that fractional weeks and months are

Log Message:
-----------
Fix interval input parser so that fractional weeks and months are
cascaded first to days and only what is leftover into seconds.  This
seems to satisfy the principle of least surprise given the general
conversion to three-part interval values --- it was an oversight that
these cases weren't dealt with in 8.1.  Michael Glaesemann

Modified Files:
--------------
    pgsql/src/backend/utils/adt:
        datetime.c (r1.169 -> r1.170)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/datetime.c.diff?r1=1.169&r2=1.170)
    pgsql/src/interfaces/ecpg/pgtypeslib:
        interval.c (r1.32 -> r1.33)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/interfaces/ecpg/pgtypeslib/interval.c.diff?r1=1.32&r2=1.33)
    pgsql/src/test/regress/expected:
        interval.out (r1.16 -> r1.17)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/interval.out.diff?r1=1.16&r2=1.17)
    pgsql/src/test/regress/sql:
        interval.sql (r1.9 -> r1.10)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/interval.sql.diff?r1=1.9&r2=1.10)