[ Resolution proposed by ballot comment: ]

Make the move constructor for atomic future lock the source

Addresses US-204

According to the definition of atomic_future, all members of atomic_future are synchronizing except constructors. However, it would probably be appropriate for a move constructor to be synchronizing on the source object. If not, the postconditions on paragraphs 7-8, might not be satisfied. This may be applicable if a collection of futures are being doled out to a set of threads that process their value.