Bug#674083: debian/rules style for python-tz

[Thomas Kluyver]

I think Barry's key suggestion was to avoid using for loops to handle
multiple versions of Python 3. The example in LibraryStyleGuide uses
rules like this:

build-python%:
        python$* setup.py build

override_dh_auto_build: $(PYTHON3:%=build-python%)
        dh_auto_build

CCed Barry in case he wants to offer other suggestions about
modernising d/rules.
For reference, the current d/rules file in Debian is here:
http://anonscm.debian.org/viewvc/pkg-zope/python-tz/trunk/debian/rules?view=markup

Thanks,
Thomas