Support for the H5FD_SPLIT driver

As suggested by the title, this adds support for the H5FD_SPLIT driver:

```python
>>> import glob, tables
>>> tables.open_file("example", mode="w", driver="H5FD_SPLIT")
File(filename=example, title=u'', mode='w', root_uep='/', filters=Filters(complevel=0, shuffle=False, fletcher32=False))
/ (RootGroup) u''
glob.glob("example*")
['example-m.h5', 'example-r.h5']
```