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.
Fixing confilcts during the rebase with hdf5_dd