Implement LMB logic for selection prompt

[obiwankimberly]

Replace the current selection prompt (form on the bottom line) with this logic:

if (is_index){  
    printf("K <keywords>, ");
    length_of_prompt = length_of_prompt + 14;
}
if (href_count!=0){
    printf("<ref.number>, ");   
    length_of_prompt = length_of_prompt + 14;
}
if (node_count>1){
    printf("Back, ");
    length_of_prompt = length_of_prompt + 6;
}
if (!end_of_file){
    printf("<RETURN> for more, ");
    length_of_prompt = length_of_prompt + 19;
}
if (length_of_prompt <= 47){
    printf("Quit, ");
}
printf("or Help: ");