Closes #926. Don't display a menu when a CPPopUpButton is right clicked, especially not a broken one.

AppKit/CPPopUpButton.j

@@ -662,7 +662,7 @@ CPPopUpButtonStatePullsDown = CPThemeState("pulls-down");
             location = CGPointMake(CGRectGetMinX(contentRect) - standardLeftMargin, 0.0);
 
         minimumWidth += standardLeftMargin;
-        
+
         // To ensure the selected item is highlighted correctly, unset the highlighted item
         [menu _highlightItemAtIndex:CPNotFound];
     }
@@ -702,6 +702,11 @@ CPPopUpButtonStatePullsDown = CPThemeState("pulls-down");
 */
 }
 
+- (void)rightMouseDown:(CPEvent)anEvent
+{
+    // Disable standard CPView behaviour which incorrectly displays the menu as a 'context menu'.
+}
+
 - (void)_popUpItemAction:(id)aSender
 {
     [self sendAction:[self action] to:[self target]];