changed prototype of

changed prototype of
union data_types * data_types_assign(NMEM nmem,
                                     union data_types * data1,
                                     union data_types data2)
to
union data_types * data_types_assign(NMEM nmem,
                                     union data_types ** data1,
                                     union data_types data2)
to make sure that side effects are transmitted outside.
added tests for side effects.
added code for proper initialization of
record->metadata[i] and record->sortkeys[i] - valgrind my your friend!