Updates UID.py and _UID_dict.py (no change) to common py2/3 code
Modernizes (py2/3 common code) main pydicom files up to (not incl) tag.py alphabetically.

Files were run through python-modernize (uses six library) with
python-modernize <filename> -wx libmodernize.fixes.fix_import,
i.e. did not force absolute import __future__ as we already use absolute everywhere

Full test suite still passes under py26, py27.
Add unittest2 import exception

A proposal to throw an error if unittest2 is not installed.
Merge pull request #159 from jrkerns/patch-1

Add unittest2 import exception
Merge branch 'dev' of https://github.com/darcymason/pydicom into dev
Merge branch 'dev' of https://github.com/jrkerns/pydicom into jrkerns-dev
Merge branch 'jrkerns-dev' into dev
Modernizes tag.py common py2/3 code.  Fixes relative import in _UID_dict
Merge pull request #164 from jrkerns/dev

A few Numpy-style docstrings and a few googlecode links fixed.
Modernizes remaining files in main code directory.
Merge pull request #166 from jrkerns/dev

Fixes documentation links and addresses issue #163
Modernizes all test suite files.  Fix for dataset.py PropertyError issue with reraise.
Merge branch 'modernize' into dev
Fix tox.ini after merge.  Further comments on 'modernize' merge in this (full) commit message.

Note 'six' module used, but (a 'to do' item) a home-grown compat module could suffice. Also needs another look at the string/unicode compatibility conversions.
Edit .travis.yml to test under python 3.3 and 3.4
Modernizes (python2/3 compatible code) the pydicom examples directory.

Added explicit __hash__ to PersonName3 class (python3.4+ needs explicit conversion for object).
Many places needed explicit bytes literal added to strings.
Unable to test dicomtree using Tix on my current platform.
Did not test interactive examples yet.
Modernizes contrib folder files.  Minimal testing done.

pydicom_PIL file cleaned up for line length, easier readability.
Merge branch 'modernize' into dev
more doc style changes