MDL-18375 calendar: prevent using the functionality in define_after_data when creating a date/time profile field

If we are adding a new profile field then the dates have already been set by setDefault
to the correct dates in the used calendar type. We only want to execute the code in
define_after_data when we have the years in the DB saved in Gregorian that need
converting to the date for this user.
MDL-18375 calendar: fixed the issue where changing calendar types and resaving the year in the date/time field caused the year to decrease.

For example, a user may create a date/time profile field and set the 'Start year' field to
'2012'. Another user, using the Hijri calendar, may edit the name of this field. They visit
the settings page and in this case the date '1/1/2012' is converted to '7/2/1433' in Hijri.
So, the year '1433' is then displayed. The user then changes the name of this field and
saves the form. This is where the issue occurs, as the date '1/1/1433' is converted into
Gregorian, which converts to the year '26/09/2011', so the year '2011' is saved in the DB,
not '2012'.