tests do not compile with g++-4.8.0-4

[Stefan Seifried]

The test do not compile with g++-4.8.0-4, libstdc++4.8.0-4, see attached compile.txt under Ubuntu 13.04.

gcc was obtained by launchpad ppa from https://launchpad.net/~ubuntu-toolchain-r/+archive/test which is suggested widely throughout the internet to get gcc 4.8 running.

However pheet does compile with warnings with g++4.7.3 on the same installation.