Localized datetime fix

Once again ran into a strange issue when using localized content. To reproduce this issue do the following:
- Set the current locale to something else than en_US
- Login with a user that has empty required attributes (so that they will be asked after login)
- When the system tries to save the attributes, they are not saved because the attribute value datetime is in incorrect format

E.g. the Zend_Date object does not know letter "i" in the datetime format which caused the system to try to save a datetime like:
2013-13-5 4:\i:5

Please also note that the other formats were incorrect as in the Zend library "m" means minute where as for the php default formatter it means a month.