fix compiling on OS X

- Fixed "#ifndef __unix__", which is not defined in all Unix OSes, in RPSSocket.h by using:

    #if !defined(__unix__) && (defined(__unix) || (defined(__APPLE__) && defined(__MACH__)))
    #define __unix__
    #endif

- Fixed compiling errors in "underTest/_4gsim" stuff by #define'ing "WITH_4GSIM" in the appropriate files, so that a required header file is properly included. It might be wise to evaluate a better fix.