Compare date/datetime #4

Comparison of dates is a string comparison at the moment. As two dates/datetimes can have two different string representations and still be equal (think timezones: 9:00pm EST and 6:00pm PST are equal, though their string representations are different).

This impacts conditions:

• equals
• doesnotequal
• isinrange
• isnotinrange
• lessthan
• lessthanorequal
• greaterthan
• greaterthanorequal
• isinset