FLEX-34880 Placed only one state setter (SortField.compareFunction) behind mx_internal (thus also renaming it to SortField.compareFunction_) to provide the template for the others. Also removed it from the interface (ISortField).
FLEX-34884 CAUSE The reason items weren't findable in a collection sorted by complex fields was that Sort.findItem() was going through the field names to make sure that all of them are present on the destination objects. This check failed for complex objects. SOLUTION Instead of checking by itself, Sort.findItem() now delegates this responsibility to the respective ISortFields. In turn, SortField and ComplexSortField can now tell Sort whether an object has a certain property and, respectively, whether an object has the first property in the chain for ComplexSortField (because any part of the chain can be null without meaning the entire chain can never be accessed - it just can't be accessed now).
NOTES -Now the previously added unit test passes. -Also note that in this way Sort.fieldList is no longer needed, which should speed up the fields setter.