Add specs for Array#keep_if, Array#select! on frozen objects
Fix Array#keep_if on frozen objects
Fix Array#select! on frozen objects
Add spec for Array#delete_if on frozen objects
Fix Array#delete_if on frozen objects
Add spec for Array#reject! on frozen objects
Fix Array#reject! on frozen objects
Merge pull request #2300 from kachick/fix-array-filters-always_return_enum

Side effect filters should return Enumerator on frozen array