reintroduction of serialization for UniqueConstant
deleted autoregister code from Variable.h and Constant.h
deleted useless UniqueConstant serialization
included PhysicalQuantitiesSerializationTest.cc
QuantityCluster.h corrected
Makefiles corrected
adapted to serialization WITHOUT autoregistration
comment on serialization autoregistration
*** empty log message ***
deleted boost serialization includes in Quantity
