[MIR] build dependencies of python-networkx

[Matthias Klose]

needs dvipng and python-pygraphviz to build the docs. instead of disabling the docs, lets promote the tools to build it:

dvipng:
 - just updated to 1.15 to fix existing bugs in Debian
 - no more bugs in Debian/Ubuntu
 - sane packaging
 - last upstream release in Feb 2015.

python-pygraphviz:
 - python library
 - maintained by the Python modules team
 - could use an update to the last released version (currently RC)

subscribed ubuntu-foundations to the bug reports for both packages.

[Matthias Klose (doko)]

dvipng was already in main until vivid.

[Michael Terry (mterry)]

In python-pygraphviz:

pygraphviz/graphviz_wrap.c: In function ‘agattr_label’:
pygraphviz/graphviz_wrap.c:3321:12: warning: return makes integer from pointer without a cast [-Wint-conversion]
     return agattr(g, kind, name, val);
            ^

That looks like a problem waiting to happen. It's in SWIG generated code, but I dig into what the source of the issue is. Any ideas on whether this is a real problem?

Otherwise, it looks fine.

[Matthias Klose (doko)]

fixed the compiler warning in 1.3.1-0ubuntu1

[Matthias Klose (doko)]

there are more universe deps to build the -doc package, so just drop the -doc package.