graphics/py-graphviz: Move to py-pygraphviz, Fix 3.x build
There are numerous graphviz related packages in PyPI, including:
graphviz, graphviz-python and pygraphviz.
This port, py-graphviz, is not and does not provide the same package
as the 'graphviz' package on PyPI (CHEESESHOP).
Further, it blocks the creation of a correctly named py-graphviz port,
the package they expect based on a standard search, and is likely to
create confusion among other ports if they depend on a python graphviz
package, which could result in incorrect packages/dependencies.
This is why among other reasons, Python packages should be named(Only the first 15 lines of the commit message are shown above )