Fix kosaraju_strongly_connected_components documentation

The output is no longer ordered in a specific way.
Merge pull request #1217 from ysitu/kosaraju_doc

Fix kosaraju_strongly_connected_components documentation
Added class GraphMLWriteLxml to support incremental generation.
Add lxml to travis
Second attempt to provide a correct travis configuration
Merge branch 'master' of https://github.com/sk-/networkx