Fix a bug with StorageNumpy
Fix a bug with StorageNumpy

    * There was a problem when making a StorageNumpy persistent, as the
    field _row_elem was not updated, and therefore a crash happens when
    the Numpy was accessed. Therefore two things are changed:
	- When the object is made_persistent, the _row_elem is updated.
	- And, when the object is instantiated (at object creation) if
	the object is in cassandra, the _row_elem is also updated
	(intead of doing this in the initialization method that will be
	redundant in the case where an object is instantiated with a
	name).

bsc-dd/hecuba,bsc-dd/hecuba,bsc-dd/hecuba,bsc-dd/hecuba