Convert Runtime.RegisterEntryAssembly to use GCHandle.

runtime/delegates.t4

@@ -83,7 +83,7 @@
 		},
 
 		new XDelegate ("void", "void", "xamarin_register_entry_assembly",
-			"MonoReflectionAssembly *", "IntPtr", "assembly"
+			"GCHandle->MonoReflectionAssembly *", "IntPtr", "assembly"
 		) {
 			WrappedManagedFunction = "RegisterEntryAssembly",
 			OnlyDynamicUsage = true,

src/ObjCRuntime/Runtime.cs

@@ -402,7 +402,7 @@ namespace ObjCRuntime {
 
 		static void RegisterEntryAssembly (IntPtr a)
 		{
-			RegisterEntryAssembly ((Assembly) ObjectWrapper.Convert (a));
+			RegisterEntryAssembly ((Assembly) GetGCHandleTarget (a));
 		}
 
 		static void ThrowNSException (IntPtr ns_exception)