allow overriding services hostname

Fixes #1407

default.yaml

     # oragono will write files to disk under certain circumstances, e.g.,
     # CPU profiling or data export. by default, these files will be written
     # to the working directory. set this to customize:
-    # output-path: "/home/oragono/out"
+    #output-path: "/home/oragono/out"
+
+    # the hostname used by "services", e.g., NickServ, defaults to "localhost",
+    # e.g., `NickServ!NickServ@localhost`. uncomment this to override:
+    #override-services-hostname: "example.network"
 
 # account options
 accounts:

irc/config.go

 			forceTrailing      bool
 			SendUnprefixedSasl bool `yaml:"send-unprefixed-sasl"`
 		}
-		isupport      isupport.List
-		IPLimits      connection_limits.LimiterConfig `yaml:"ip-limits"`
-		Cloaks        cloaks.CloakConfig              `yaml:"ip-cloaking"`
-		SecureNetDefs []string                        `yaml:"secure-nets"`
-		secureNets    []net.IPNet
-		supportedCaps *caps.Set
-		capValues     caps.Values
-		Casemapping   Casemapping
-		EnforceUtf8   bool         `yaml:"enforce-utf8"`
-		OutputPath    string       `yaml:"output-path"`
-		IPCheckScript ScriptConfig `yaml:"ip-check-script"`
+		isupport                 isupport.List
+		IPLimits                 connection_limits.LimiterConfig `yaml:"ip-limits"`
+		Cloaks                   cloaks.CloakConfig              `yaml:"ip-cloaking"`
+		SecureNetDefs            []string                        `yaml:"secure-nets"`
+		secureNets               []net.IPNet
+		supportedCaps            *caps.Set
+		capValues                caps.Values
+		Casemapping              Casemapping
+		EnforceUtf8              bool         `yaml:"enforce-utf8"`
+		OutputPath               string       `yaml:"output-path"`
+		IPCheckScript            ScriptConfig `yaml:"ip-check-script"`
+		OverrideServicesHostname string       `yaml:"override-services-hostname"`
 	}
 
 	Roleplay struct {

irc/server.go

 		} else if oldConfig.Server.IPCheckScript.MaxConcurrency != config.Server.IPCheckScript.MaxConcurrency ||
 			oldConfig.Accounts.AuthScript.MaxConcurrency != config.Accounts.AuthScript.MaxConcurrency {
 			return fmt.Errorf("Cannot change max-concurrency for scripts after launching the server, rehash aborted")
+		} else if oldConfig.Server.OverrideServicesHostname != config.Server.OverrideServicesHostname {
+			return fmt.Errorf("Cannot change override-services-hostname after launching the server, rehash aborted")
 		}
 	}
 
 		if maxAuthConc != 0 {
 			server.semaphores.AuthScript.Initialize(maxAuthConc)
 		}
+
+		if err := overrideServicePrefixes(config.Server.OverrideServicesHostname); err != nil {
+			return err
+		}
 	}
 
 	if oldConfig != nil {

irc/services.go

 	}
 }
 
+func overrideServicePrefixes(hostname string) error {
+	if hostname == "" {
+		return nil
+	}
+	if !utils.IsHostname(hostname) {
+		return fmt.Errorf("`%s` is an invalid services hostname", hostname)
+	}
+	for _, serv := range OragonoServices {
+		serv.prefix = fmt.Sprintf("%s!%s@%s", serv.Name, serv.Name, hostname)
+	}
+	return nil
+}
+
 func initializeServices() {
 	// this modifies the global Commands map,
 	// so it must be called from irc/commands.go's init()

traditional.yaml

     # oragono will write files to disk under certain circumstances, e.g.,
     # CPU profiling or data export. by default, these files will be written
     # to the working directory. set this to customize:
-    # output-path: "/home/oragono/out"
+    #output-path: "/home/oragono/out"
+
+    # the hostname used by "services", e.g., NickServ, defaults to "localhost",
+    # e.g., `NickServ!NickServ@localhost`. uncomment this to override:
+    #override-services-hostname: "example.network"
 
 # account options
 accounts: