Make has(feed) a Container protocol method.

Frameworks/Account/Account.swift

@@ -615,10 +615,6 @@ public final class Account: DisplayNameProvider, UnreadCountProvider, Container,
 		}
 	}
 
-	public func has(_ feed: Feed) -> Bool {
-		return flattenedFeeds().contains(feed)
-	}
-
 	// MARK: - Container
 
 	public func flattenedFeeds() -> Set<Feed> {
@@ -653,6 +649,10 @@ public final class Account: DisplayNameProvider, UnreadCountProvider, Container,
 		postChildrenDidChangeNotification()
 	}
 	
+	public func has(_ feed: Feed) -> Bool {
+		return flattenedFeeds().contains(feed)
+	}
+
 	// MARK: - Debug
 
 	public func debugDropConditionalGetInfo() {

Frameworks/Account/Container.swift

@@ -33,6 +33,7 @@ public protocol Container: class {
 
 	//Recursive — checks subfolders
 	func flattenedFeeds() -> Set<Feed>
+	func has(_ feed: Feed) -> Bool
 	func hasFeed(with feedID: String) -> Bool
 	func hasFeed(withURL url: String) -> Bool
 	func existingFeed(with feedID: String) -> Feed?

Frameworks/Account/Folder.swift

@@ -102,6 +102,10 @@ public final class Folder: DisplayNameProvider, Renamable, Container, UnreadCoun
 		postChildrenDidChangeNotification()
 	}
 
+	public func has(_ feed: Feed) -> Bool {
+		return flattenedFeeds().contains(feed)
+	}
+
 	// MARK: - Hashable
 
 	public func hash(into hasher: inout Hasher) {