nTox: enforce friend name null termination, reduce memory loss, allow nickchange as oldname=>newname

nTox.c:
- wrap():
  * fixed still testing for 0 instead of current line start
  * removed early newline after an unbreakable line
- multiple places: tox_getname() doesn't terminate the string, make sure nTox does
- format_message():
  * renamed to print_formatted_message()
  * changed semantics: does the new_line() itself, saves caller from freeing the buffer (which no caller did)
  * changed signature: now also prints the friend's name when sending
  * intern: date is only printed once, the message line gets only time
- print_message(): enforce null termination
- main():
  * setlocale() to init locale (for date/time printing)
  * own name: ensure null termination

Messenger.c:
- notify of friend name change *before* the old name is overwritten