Add comment explaining possible compiler warning:

Add comment explaining possible compiler warning:

    /*
     *  Some compilers with throw a warning knowing this test can never be
     *  true because off_t can't exceed the compared maximum.
     */
    if (th->fileLen > MAX_TAR_MEMBER_FILELEN)
        die_horribly(AH, modulename, "archive member too large for tar format\n");