G-LINES: Forbid remote modifications if "AllowRemoteOper" is not set

G-LINES: Forbid remote modifications if "AllowRemoteOper" is not set

Explicitely forbid remote servers to modify "x-lines" (G-LINES) when the
"AllowRemoteOper" configuration option isn't set, even when the command
seems to originate from the remote server itself: this prevents GLINE's
to become set during server handshake in this case (what wouldn't be
possible during regular runtime when a remote IRC Op sends the command)
and what can't be undone by IRC Ops later on (because of the missing
"AllowRemoteOper" option) ...