Add a key to delete to end of line at the prompt (^K in emacs mode, C/D in vi).

From Kalle Olavi Niemitalo.

mode-key.c

@@ -110,6 +110,12 @@ mode_key_lookup_vi(struct mode_key_data *mdata, int key)
 		return (MODEKEYCMD_BACKTOINDENTATION);
 	case '\033':
 		return (MODEKEYCMD_CLEARSELECTION);
+	case 'C':
+		if (mdata->flags & MODEKEY_CANEDIT)
+			mdata->flags |= MODEKEY_EDITMODE;
+		return (MODEKEYCMD_DELETETOENDOFLINE);
+	case 'D':
+		return (MODEKEYCMD_DELETETOENDOFLINE);
 	case 'j':
 	case KEYC_DOWN:
 		return (MODEKEYCMD_DOWN);
@@ -169,6 +175,8 @@ mode_key_lookup_emacs(struct mode_key_data *mdata, int key)
 	case '\027':
 	case 'w' | KEYC_ESCAPE:
 		return (MODEKEYCMD_COPYSELECTION);
+	case '\013':
+		return (MODEKEYCMD_DELETETOENDOFLINE);
 	case '\016':
 	case KEYC_DOWN:
 		return (MODEKEYCMD_DOWN);

status.c

@@ -823,6 +823,12 @@ status_prompt_key(struct client *c, int key)
 			c->flags |= CLIENT_STATUS;
 		}
 		break;
+	case MODEKEYCMD_DELETETOENDOFLINE:
+		if (c->prompt_index < size) {
+			c->prompt_buffer[c->prompt_index] = '\0';
+			c->flags |= CLIENT_STATUS;
+		}
+		break;
 	case MODEKEYCMD_UP:
 		if (server_locked)
 			break;

tmux.1

@@ -331,6 +331,7 @@ The following keys are supported as appropriate for the mode:
 .It Li "Cursor right" Ta "l" Ta "Right"
 .It Li "Start selection" Ta "Space" Ta "C-Space"
 .It Li "Cursor up" Ta "k" Ta "Up"
+.It Li "Delete to end of line" Ta "D or C" Ta "C-k"
 .It Li "Paste buffer" Ta "p" Ta "C-y"
 .El
 .Pp

tmux.h

@@ -365,6 +365,7 @@ enum mode_key_cmd {
 	MODEKEYCMD_COMPLETE,
 	MODEKEYCMD_COPYSELECTION,
 	MODEKEYCMD_DELETE,
+	MODEKEYCMD_DELETETOENDOFLINE,
 	MODEKEYCMD_DOWN,
 	MODEKEYCMD_ENDOFLINE,
 	MODEKEYCMD_LEFT,