compatibility fixes for compiling under Objective C++

If you have a project wherein you include MKNetworkKit, and under project settings, "Compile source as.." is set to Objective C++, using LLVM, some errors pop up which break the build. 
These changes address those errors.

I made a small test harness here https://github.com/ralph-e-boy/mknetworktests
but noticed that you have a full test suite so I stopped working on that one.

--ralph-e-boy