Fix compiler warnings

T here are some more controversial commits hidden here. Have a longer stare at 80be45043c94c95dc198a01403b66446f6ceec26 200d8c6d2947de6cc7a20ac2c9e5bc8f50eb78a9 and e7148817c2b565906d553b6595a678170116ac09.

Besides, see this [issue](https://github.com/rock-core/tools-pocolog_cpp/issues/2) which is more or less related to 80be45043c94c95dc198a01403b66446f6ceec26.