Bring back the transclusion.  Close #285.

The workaround to prevent issue #90 is revealed here, after
fair amount of googling:

    https://github.com/angular/angular.js/issues/5703

Since Angular 1.2.1 we can pass $scope as first argument to
$transclude, to prevent it from creating a new scope.

We now require Angular >= 1.2.1.