caused some strange problems on NT. crashed if the test for the compound type
was second when called from the command line but not if i clicked on the icon.
strange but this seemed to make it better
H5Tconvert calls.
Added tests to tvltypes.c which test arrays of VL compound datatypes,
array of compound datatypes with VL fields and arrays of nested VL sequences
of VL sequences of atomic types, all of which are working correctly.
