Fix unreliable tests uncovered by IronPython
Make katz_centrality compatible with IronPython
Make add_nodes_from compatible with IronPython
Fix I/O compatibility with IronPython
Fix I/O compatibility with IronPython (cont'd)
Reapply "correct minor typos in edgelist.py"

This reapplies commit d189147, which was inadvertently reverted in
commit 002d537.
Work around IronPython issue with compile()

IronPython does not recognize __future__.CO_FUTURE_PRINT_FUNCTION passed
as flags to compile(). Doctests automatically pass this flag when
print_function is imported from __future__.
Make find_cliques/find_cliques_recursive compatible with IronPython

The implementations are replaced with more straightforward and concise
versions as described by Tomita, Tanaka and Takahashi.
Install enum34 for testing with IronPython on Travis
Avoid using /tmp when installing dependencies for testing with IronPython on Travis
Merge pull request #1211 from ysitu/ipy

Fix numerous compatibility issues with IronPython