pkexec: improve pkexec authentication message

Instead of the program variable, output the command_line.

If is the length of a command_line bigger than 80 characters, output is: "{first 38 chars from the CL} ... {last 42 chars from the CL}"

Commented code:

    if (strlen(command_line) > 80 ) {
        char buff[80];
        // The memset() function fills the first n bytes of the memory area
        // pointed to by s with the constant byte c.
        memset(buff, 0, strlen(buff));
        
        // declares a char array of size 6 and initializes it with the characters ' ', '.', '.', '.', ' ' and '\0'
        char delim[] = " ... "; 

        // char *strncpy(char *dest, const char *src, size_t n);        
        // Warning: If there is no null byte among the
        // first n bytes of src, the string placed in dest will not be null-
        // terminated.

        // copy the first 37 chars from CL into the buff
        strncpy(buff, command_line, 38);

        // copy the delimiter into the buff
        strncpy(buff + 38, delim, 5);

        // copy the last 38 chars from CL into the buff
        strncpy(buff + 43, command_line +
                strlen(command_line) - 37,
                38);

        // copy the buff into the command_line
        strncpy(command_line, buff, 80);

        // The memset() function fills the first n bytes of the memory area
        // pointed to by s with the constant byte c.
        memset(command_line + 80, 0, strlen(command_line) - 80);
    }