Defensive programming against buffer overflow

[Tygre]

As per the advice in the Unix Network Programming Book, p.15, replace:

1. sprintf with snprintf

2. gets with fgets

3. strcat with strncat (or strlcat)

4. strcpy with strncpy (or strlcpy)

[Tygre]

Finally, I took the time to replace all strcpy() and strcat() with snprintf() (my version...) and strncpy() (my version) and strncat()...