Introduced by 61f3e3e29, as part of my periodic efforts to make the
GTK front end work usefully on OS X: the 'Unable to open connection to
[host]: [error]' message box is accidentally passed through two layers
of printf format-string parsing, the second of which has no argument
list. So if you pass in a host name like '%s' on the command line,
bad things will happen when that error message is constructed.
This happened because in that commit I changed a call to
fatal_message_box() into a call to connection_fatal(), without
noticing that the latter was printf-style variadic and the former
wasn't. On the plus side, that means now I can remove the explicit
dupprintf/free around the error message.
921613ff08