Clocktables: Fix display of ISO week.

Clocktables: Fix display of ISO week.

David Bremner writes:

    I have a clocktable that begins like this.

    #+BEGIN: clocktable :maxlevel 2 :block 2009-W05 :scope agenda-with-archives
    Clock summary at [2009-01-27 Tue 17:15], for week 2009-W04.

    [contents snipped]

    #+END:

    Whatever week I put in :block, it puts one less in the title.  It
    seems actually gather the clock data from the right week, but the
    title is wrong?  Or I misunderstand something as usual :-).

There was a problem wit the week starting date.