update to 3.5.7

* [Fixed] Fix sub field default value - http://support.advancedcustomfields.com/discussion/3706/select-field-default-value-not-working
* [Added] Add filters for custom location rules - http://support.advancedcustomfields.com/discussion/4285/how-to-retrieve-a-custom-field-within-the-function-php
* [Fixed] Fix XML import to create unique field ID's - http://support.advancedcustomfields.com/discussion/4328/check-acf_next_field_id-to-avoid-data-corruption
* [Fixed] Fix conditional logic with validation - http://support.advancedcustomfields.com/discussion/4295/issue-with-conditional-logic-and-obrigatory-fields
* [Fixed] Fix repeater + relationship bug - http://support.advancedcustomfields.com/discussion/4296/relationship-field-bug

Signed-off-by: Elliot Condon <e@elliotcondon.com>