Added the DataDescriptor for HDF5
First test for HDF5 passing
Adding a more complete test suite (still a failure is going on)
Skip HDF5 tests if pytables is not found
Making PyTables actually optional
Using contexts for file handling as much as possible
Updated test for dealing with scalar conversions with struct arrays and dynd
Adding pytables to the list of packages for running tests
Closing the stale handle that returns mkstemp
Added a small comment on why we close the file handle
Actually doing a flush() after the append
The flush was not really necessary.
Better test avoid the aribitrary order of the fields