Troca integração do py.test com ipdb pelo pdb++

O plugin pytest-ipdb foi descontinuado e o
pdb++ se integra automaticamente com o py.test

Vide:
 https://github.com/mverteuil/pytest-ipdb#notice
 https://pypi.python.org/pypi/pdbpp

requirements/dev-requirements.txt

@@ -1,9 +1,10 @@
 -r test-requirements.txt
+
 autopep8==1.2.4
 beautifulsoup4==4.6.0
 django-debug-toolbar==1.5
 ipdb==0.10.1
+pdbpp==0.9.2
 pip-review==0.4
-pygraphviz==1.3.1
-pytest-ipdb==0.1-prerelease2
 pipdeptree==0.10.1
+pygraphviz==1.3.1