Fixed and/or problem in dobj.__lt and dobj.__le

This snippet demonstrates the problem:

local date = require "date"
local a = date("20131230 00:57:04")
local b = date("20131230 01:00:00")
print(a >= b) -- should be false
Merge pull request #3 from clarkjc/master

Fixed and/or problem in dobj.__lt and dobj.__le