swanctl: Check for conflicts with shared options when registering commands

Also suppress errors when pre-processing shared options (this was missing
here but already used in pki).

src/swanctl/command.c

@@ -185,6 +185,8 @@ static bool process_common_opts(bool init)
 	int prevoptind = optind;
 	bool success = TRUE;
 
+	/* don't report any errors during this pre-processing */
+	opterr = 0;
 	while (TRUE)
 	{
 		switch (getopt_long(argc, argv, command_optstring, command_opts, NULL))
@@ -243,6 +245,16 @@ void command_register(command_t command)
 			return;
 		}
 	}
+	for (i = 0; i < countof(shared_options); i++)
+	{
+		if (shared_options[i].op == command.op)
+		{
+			fprintf(stderr, "unable to register command --%s, short option "
+					"-%c conflicts with --%s\n", command.cmd, command.op,
+					shared_options[i].name);
+			return;
+		}
+	}
 
 	cmds[registered] = command;
 	/* append default options, but not to --help */