convert ‘popoverVisible’ to more closely mirror the UIPopoverController API

Author: hsoi

WYPopoverController/WYPopoverController.h

@@ -95,7 +95,7 @@ typedef NS_OPTIONS(NSUInteger, WYPopoverAnimationOptions) {
 @property (nonatomic, copy) NSArray *passthroughViews;
 @property (nonatomic, assign) BOOL wantsDefaultContentAppearance;
 @property (nonatomic, assign) UIEdgeInsets popoverLayoutMargins;
-@property (nonatomic, assign, readonly) BOOL isPopoverVisible;
+@property (nonatomic, assign, readonly, getter = isPopoverVisible) BOOL popoverVisible;
 @property (nonatomic, strong, readonly) UIViewController* contentViewController;
 @property (nonatomic, assign) CGSize popoverContentSize;
 

WYPopoverController/WYPopoverController.m

@@ -1371,7 +1371,7 @@ @implementation WYPopoverController
 @synthesize delegate;
 @synthesize passthroughViews;
 @synthesize wantsDefaultContentAppearance;
-@synthesize isPopoverVisible;
+@synthesize popoverVisible;
 @synthesize popoverLayoutMargins;
 
 - (id)initWithContentViewController:(UIViewController *)aViewController