[messageui] Update for iOS 10 beta 1 & 3 (#431)

The enums are not untyped anymore but are NSInteger.

src/MessageUI/MessageUI.cs

@@ -12,23 +12,41 @@ using XamCore.ObjCRuntime;
 
 namespace XamCore.MessageUI {
 
-	// untyped enum -> MFMailComposeViewController.h
+#if XAMCORE_4_0
+	[Native]
+	public enum MFMailComposeResult : nint {
+#else
+	// Before iOS 10 beta 3, this was an untyped enum -> MFMailComposeViewController.h
+	// Note: now used as a NSInteger in the API.
 	public enum MFMailComposeResult {
+#endif
 		Cancelled,
 		Saved,
 		Sent,
 		Failed
 	}
 
-	// untyped enum -> MFMailComposeViewController.h
 	[ErrorDomain ("MFMailComposeErrorDomain")]
+#if XAMCORE_4_0
+	[Native]
+	public enum MFMailComposeErrorCode : nint {
+#else
+	// Before iOS 10 beta 3, this was an untyped enum -> MFMailComposeViewController.h
+	// Note: now used as a NSInteger in the API.
 	public enum MFMailComposeErrorCode {
+#endif
 	    SaveFailed,
 	    SendFailed
 	}
 
-	// untype enum -> MFMessageComposeViewController.h
+#if XAMCORE_4_0
+	[Native]
+	public enum MessageComposeResult : nint {
+#else
+	// Before iOS 10 beta 3, this was an untyped enum -> MFMessageComposeViewController.h
+	// Note: now used as a NSInteger in the API.
 	public enum MessageComposeResult {
+#endif
 		Cancelled, Sent, Failed
 	}
 }

src/messageui.cs

@@ -12,6 +12,7 @@ using System;
 using XamCore.ObjCRuntime;
 using XamCore.Foundation;
 using XamCore.CoreFoundation;
+using XamCore.Messages;
 using XamCore.UIKit;
 
 namespace XamCore.MessageUI {
@@ -104,6 +105,10 @@ namespace XamCore.MessageUI {
 		[Export ("attachments")]
 		NSDictionary[] GetAttachments ();
 
+		[iOS (10,0)]
+		[NullAllowed, Export ("message", ArgumentSemantic.Copy)]
+		MSMessage Message { get; set; }
+
 		[Since (7,0)]
 		[Export ("addAttachmentURL:withAlternateFilename:")]
 		bool AddAttachment (NSUrl attachmentURL, [NullAllowed] string alternateFilename);