Update later.js

was failing with test
var newDate = new Date('2014-02-28');
later.schedule({schedules: [{D:[1], M:[2], Y:[2014]},{D_a:[27], D_b:[29], M:[2], Y:[2014]}], exceptions: []}).isValid(newDate);

return !b || a.getTime() > b.getTime();   <-- a is null and so a.getTime() is blowing up

Bills fix is working a treat so far
You'll want to make these changes in schedule.js, around line 338.  You can then run 'make' to build later.js and test it.