Tweaked css so sibling tests sections aren't all styled as not-implemented.
Fix for error triggered by empty tests section.

Something like this triggers it:
  tests = with_tests('widget tests',function(M){
    ...
    M.tests('make',function(M){
    });
  });

Problem is in treewalk
      ...
      if(sweep) {
        module.each(tests.items,function(item){
          sweep(tests,item);
        });
      }
      ...
tests.items is empty.
So sweep never gets called.
So tests.cumulative never gets initialized.

We now initialize when creating the datastructure.