[gc] fix one gc heisenbug, although apparently this isn't the only one. When cloning an object, we get into situations where we mark the object before it's ATTRs struct is initialized. This causes whatever garbage was in that allocated memory to be passed to the GC for marking, and hilarity ensues. Zero out the struct here to ensure we have NULL values in the struct and then Parrot_Object_mark won't try to mark the NULL pointers
[gc] fix one gc heisenbug, although apparently this isn't the only one. When cloning an object, we get into situations where we mark the object before it's ATTRs struct is initialized. This causes whatever garbage was in that allocated memory to be passed to the GC for marking, and hilarity ensues. Zero out the struct here to ensure we have NULL values in the struct and then Parrot_Object_mark won't try to mark the NULL pointers

git-svn-id: 6e74a02f85675cec270f5d931b0f6998666294a3@39879 d31e2699-5ff4-0310-a27c-f18f2fbe73fe

gagern/parrot,fernandobrito/parrot,tewk/parrot-select,tkob/parrot,tkob/parrot,gagern/parrot,gagern/parrot,gitster/parrot,gitster/parrot,youprofit/parrot,youprofit/parrot,FROGGS/parrot,fernandobrito/parrot,youprofit/parrot,tkob/parrot,parrot/parrot,fernandobrito/parrot,parrot/parrot,tewk/parrot-select,fernandobrito/parrot,tkob/parrot,fernandobrito/parrot,gagern/parrot,gagern/parrot,youprofit/parrot,gitster/parrot,fernandobrito/parrot,parrot/parrot,gagern/parrot,FROGGS/parrot,FROGGS/parrot,tewk/parrot-select,youprofit/parrot,youprofit/parrot,FROGGS/parrot,tkob/parrot,FROGGS/parrot,gitster/parrot,gitster/parrot,tewk/parrot-select,tkob/parrot,tkob/parrot,youprofit/parrot,FROGGS/parrot,tkob/parrot,tewk/parrot-select,tewk/parrot-select,parrot/parrot,gagern/parrot,gitster/parrot,gitster/parrot,fernandobrito/parrot,FROGGS/parrot,FROGGS/parrot,parrot/parrot,youprofit/parrot,tewk/parrot-select