ChunkedIterator for Traversable - Fixed
ChunkedIterator valid is a bool of chunk

Just some minor code cleanup. The negation of empty is just not necessary and rather clumsy.
ChunkedIterator missing value check

Minor change to implement a size equal or greate zero. Also
enforce integer type to make the behavior more distinct.
FilterIterator expects Iterator not Traversable - Fixed

SPL's FilterIterator does take an Iterator in it's constructor,
not a Traversable. This minor change corrects the type-hint used.
Merge pull request #417 from hakre/patch-2

ChunkedIterator for Traversable