Code review comment for lp:~widelands-dev/widelands/compiler_warnings_062017

Ahh, thanks for starting this branch.

I will start with these two:

compiler_warnings_062017/src/scripting/lua_errors.h:27:7: warning: 'LuaError' has no out-of-line virtual method
      definitions; its vtable will be emitted in every translation unit [-Wweak-vtables]
class LuaError : public WException {
      ^
compiler_warnings_062017/src/scripting/lua_errors.h:32:7: warning: 'LuaScriptNotExistingError' has no out-of-line virtual
      method definitions; its vtable will be emitted in every translation unit [-Wweak-vtables]
class LuaScriptNotExistingError : public LuaError {