When calling clocktable with :block *month and :step week it splits into
block 7 days long starting from the first day in the month... that's not
very useful I think, so here is a patch making it split the month into
weeks starting on mondays.  The first and last week will be clipped to only
include the days in the selected month and as such will not contain the
full 7 days of those weeks.

-- 
  Peder Stray