Work-around for Eclipse bug regarding EnumSets

This commit introduces superfluous casts in CollectionFactory to
address a bug in Eclipse 4.4.1 that prevents the code from compiling
within Eclipse. Specifically, without these casts Eclipse displays the
following error for use of the EnumSet.copyOf() and EnumSet.noneOf()
methods:

Type mismatch: cannot convert from EnumSet<Enum<Enum<E>>> to
Collection<E>