Fixed a bug where having just the year as a date would cause an exception
to be thrown. This was happening because the call to .val() was returning
an integer in these cases. This would cause problems later on when we
tried to invoke string methods, like match, on the returned value. To fix
the problem, we're just now explicitly converting to a string.
Added methods to allow changing the format, minViewMode, and viewMode of
the date picker after it's been created