Stop sending release events for mouse wheel 'buttons' in X mouse mode.

On Windows (X mouse reporting of the mouse wheel isn't currently done
by the Unix front end, though I'm shortly about to fix that too) a
mouse wheel event is translated into a virtual button, and we send
both a press and a release of that button to terminal.c, which encodes
both in X mouse reporting escape sequences and passes them on to the
server. This isn't consistent with what xterm does - scroll-wheel
events are encoded _like_ button presses, but differ semantically in
that they don't have matching releases. So we're updating to match
xterm.

[originally from svn r10138]

terminal.c

@@ -5896,7 +5896,7 @@ void term_mouse(Terminal *term, Mouse_Button braw, Mouse_Button bcooked,
      */
     if (raw_mouse &&
 	(term->selstate != ABOUT_TO) && (term->selstate != DRAGGING)) {
-	int encstate = 0, r, c;
+	int encstate = 0, r, c, wheel;
 	char abuf[32];
 	int len = 0;
 
@@ -5905,22 +5905,35 @@ void term_mouse(Terminal *term, Mouse_Button braw, Mouse_Button bcooked,
 	    switch (braw) {
 	      case MBT_LEFT:
 		encstate = 0x00;	       /* left button down */
+                wheel = FALSE;
 		break;
 	      case MBT_MIDDLE:
 		encstate = 0x01;
+                wheel = FALSE;
 		break;
 	      case MBT_RIGHT:
 		encstate = 0x02;
+                wheel = FALSE;
 		break;
 	      case MBT_WHEEL_UP:
 		encstate = 0x40;
+                wheel = TRUE;
 		break;
 	      case MBT_WHEEL_DOWN:
 		encstate = 0x41;
+                wheel = TRUE;
 		break;
-	      default: break;	       /* placate gcc warning about enum use */
+	      default:
+                return;
 	    }
-	    switch (a) {
+            if (wheel) {
+                /* For mouse wheel buttons, we only ever expect to see
+                 * MA_CLICK actions, and we don't try to keep track of
+                 * the buttons being 'pressed' (since without matching
+                 * click/release pairs that's pointless). */
+                if (a != MA_CLICK)
+                    return;
+            } else switch (a) {
 	      case MA_DRAG:
 		if (term->xterm_mouse == 1)
 		    return;
@@ -5937,7 +5950,8 @@ void term_mouse(Terminal *term, Mouse_Button braw, Mouse_Button bcooked,
 		    return;
 		term->mouse_is_down = braw;
 		break;
-	      default: break;	       /* placate gcc warning about enum use */
+              default:
+                return;
 	    }
 	    if (shift)
 		encstate += 0x04;

windows/window.c

@@ -3248,10 +3248,6 @@ static LRESULT CALLBACK WndProc(HWND hwnd, UINT message,
 				   TO_CHR_X(p.x),
 				   TO_CHR_Y(p.y), shift_pressed,
 				   control_pressed, is_alt_pressed());
-			term_mouse(term, b, translate_button(b),
-				   MA_RELEASE, TO_CHR_X(p.x),
-				   TO_CHR_Y(p.y), shift_pressed,
-				   control_pressed, is_alt_pressed());
 		    } /* else: not sure when this can fail */
 		} else {
 		    /* trigger a scroll */