RF: fix dft for Python 3, maybe latest Pydicom

dft was relying on integer division - make explicit for Python 3.

The Patient Name parameter was not coming back as a string, as dft
appeared to expect.  Maybe this changed in pydicom; in any case make
str() explicit for Patient Name.
RF: update to DICOM canonical names

Needs pydicom >= 0.9.7.  This is already the required version stated in
`info.py`
RF: replace future imports with Python 3 versions

Replace python 2.5 with_statement future imports with standard Python 3
future imports.