Move RBLPopoverWindow's implementation down to where others are.

Rebel/RBLPopover.m

@@ -19,14 +19,6 @@
 
 @end
 
-@implementation RBLPopoverWindow
-
-- (BOOL)isKeyWindow {
-	return YES;
-}
-
-@end
-
 //***************************************************************************
 
 @interface RBLPopoverBackgroundView ()
@@ -103,6 +95,16 @@ static NSTimeInterval const RBLPopoverDefaultFadeDuration = 0.3;
 
 //***************************************************************************
 
+@implementation RBLPopoverWindow
+
+- (BOOL)isKeyWindow {
+	return YES;
+}
+
+@end
+
+//***************************************************************************
+
 @implementation RBLPopover
 
 - (instancetype)initWithContentViewController:(NSViewController *)viewController {