Merge lp:~widelands-dev/widelands/bug-1830376-lanless-lan-game into lp:widelands

[Notabilis]

Use the loopback network interface for LAN announcements.

Allow the loopback network interface for LAN announcements, making it possible to use the LAN mode locally even when the network is disconnected.

Bonus fix: LAN games running on the same host now appear in the LAN lobby.
Also fixing missing whitespace in two error messages.

[GunChleoc (gunchleoc)]

Tested and working :)

@bunnybot merge

review: Approve

[bunnybot (widelandsofficial)]

Continuous integration builds have changed state:

Travis build 5122. State: passed. Details: https://travis-ci.org/widelands/widelands/builds/540162792.
Appveyor build 4904. State: failed. Details: https://ci.appveyor.com/project/widelands-dev/widelands/build/_widelands_dev_widelands_bug_1830376_lanless_lan_game-4904.

=== modified file 'src/network/network_lan_promotion.cc'
--- src/network/network_lan_promotion.cc	2019-02-23 11:00:49 +0000
+++ src/network/network_lan_promotion.cc	2019-06-01 17:25:24 +0000
@@ -102,7 +102,7 @@
 	for (ifa = ifaddr, n = 0; ifa != nullptr; ifa = ifa->ifa_next, n++) {
 		if (ifa->ifa_addr == nullptr)
 			continue;
-		if (!(ifa->ifa_flags & IFF_BROADCAST) && !(ifa->ifa_flags & IFF_MULTICAST))
+		if (!(ifa->ifa_flags & IFF_LOOPBACK) && !(ifa->ifa_flags & IFF_BROADCAST) && !(ifa->ifa_flags & IFF_MULTICAST))
 			continue;
 		switch (ifa->ifa_addr->sa_family) {
 		case AF_INET:
@@ -291,7 +291,7 @@
 			// Remove this interface id from the set
 			it = interface_indices_v6.erase(it);
 			if (interface_indices_v6.empty()) {
-				log("[LAN] Warning: No more multicast capable IPv6 interfaces."
+				log("[LAN] Warning: No more multicast capable IPv6 interfaces. "
 				    "Other LAN players won't find your game.\n");
 			}
 		} else {
@@ -359,7 +359,7 @@
 	throw WLWarning(_("Failed to use the local network!"),
 	                /** TRANSLATORS: %s is a list of alternative ports with "or" */
 	                _("Widelands was unable to use the local network. "
-	                  "Maybe some other process is already running a server on port %s"
+	                  "Maybe some other process is already running a server on port %s "
 	                  "or your network setup is broken."),
 	                i18n::localize_list(ports_list, i18n::ConcatenateWith::OR).c_str());
 }