Hdf5 xml

I have added a test IOC that I have been using to run tests, which includes two sample XML layout files.  The interface to specify the XML definition file has been improved, with only a single PV required to specify the full file name and path.  The file is checked for existence and then verified using the XML parser before the HDF writer is started, and whenever the file is changed.  Finally, a bugfix has been included to ensure the output file is closed once the data has been written.