patch 8.2.0591: MS-Windows: should always support IPv6

Problem:    MS-Windows: should always support IPv6
Solution:   Add build flag. (Ozaki Kiichi, closes #5944)
diff --git a/src/Make_cyg_ming.mak b/src/Make_cyg_ming.mak
index 091102e..d767c79 100644
--- a/src/Make_cyg_ming.mak
+++ b/src/Make_cyg_ming.mak
@@ -624,7 +624,7 @@
 endif
 
 ifeq ($(CHANNEL),yes)
-DEFINES += -DFEAT_JOB_CHANNEL
+DEFINES += -DFEAT_JOB_CHANNEL -DFEAT_IPV6
 endif
 
 ifeq ($(TERMINAL),yes)
diff --git a/src/Make_mvc.mak b/src/Make_mvc.mak
index fa14c9e..e95a94a 100644
--- a/src/Make_mvc.mak
+++ b/src/Make_mvc.mak
@@ -467,7 +467,7 @@
 !if "$(CHANNEL)" == "yes"
 CHANNEL_PRO	= proto/channel.pro
 CHANNEL_OBJ	= $(OBJDIR)/channel.obj
-CHANNEL_DEFS	= -DFEAT_JOB_CHANNEL
+CHANNEL_DEFS	= -DFEAT_JOB_CHANNEL -DFEAT_IPV6
 
 NETBEANS_LIB	= WSock32.lib Ws2_32.lib
 !endif
diff --git a/src/version.c b/src/version.c
index ee4608b..e6eadca 100644
--- a/src/version.c
+++ b/src/version.c
@@ -747,6 +747,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    591,
+/**/
     590,
 /**/
     589,