When converting a datetime field to date, using the widget date,
the date time value was just cropped, removing the hours,
therefore ignoring the user time zone.
For instance, if the user was in UTC + 1, for a date time 02/02/2015 00:30:00,
applying the widget date on this datetime had as result 02/01/2015,
due to the fact the UTC value of the datetime field was 02/01/2015 23:30:00
fixes#4420
opw-621281
2a162d9be7