Add blank +K (norepeat) chmode, though it does nothing yet.

help/opers/cmode

@@ -39,6 +39,8 @@ NO PARAMETERS:
               50% capital letters will be blocked.
      +J     - Prevent autorejoin on kick. Users will not be able to
               rejoin immediately after being kicked. 
+     +K     - No repeat messages. Messages that are the same as the
+              last message sent to the channel will be blocked.
 
 WITH PARAMETERS:
      +f     - Forward.  Forwards users who cannot join because of +i,

include/channel.h

@@ -181,6 +181,7 @@ typedef int (*ExtbanFunc)(const char *data, struct Client *client_p,
 #define MODE_NONICK	0x128000 /* Disable /nick for anyone on this channel */
 #define MODE_NOCAPS	0x256000 /* Block messages in all capital letters */
 #define MODE_NOREJOIN	0x512000 /* Block rejoin immediately after kick */
+#define MODE_NOREPEAT	0x1024000 /* Block repeat messages */
 
 #define CHFL_BAN        0x10000000	/* ban channel flag */
 #define CHFL_EXCEPTION  0x20000000	/* exception to ban channel flag */

src/chmode.c

@@ -1607,7 +1607,7 @@ struct ChannelMode chmode_table[256] =
   {chm_nosuch,	0 },			/* H */
   {chm_ban,	CHFL_INVEX },           /* I */
   {chm_simple,	MODE_NOREJOIN },	/* J */
-  {chm_nosuch,	0 },			/* K */
+  {chm_simple,	MODE_NOREPEAT },	/* K */
   {chm_staff,	MODE_EXLIMIT },		/* L */
   {chm_nosuch,	0 },			/* M */
   {chm_simple,	MODE_NONICK },		/* N */