Compare to interface not impl for CompositeData

checking for CompositeDataSupport is more specific than it needs to be. (The next line casts the value to "CompositeData") - this change will allow certain Gc fields to be parsed properly that implement CompositeData but do not extend CompositeDataSupport
Merge pull request #70 from ryangardner/master

Minor fix: check for CompositeData instead of CompositeDataSupport