Made the Win10 share work, at least somewhat.

GreenshotWin10Plugin/Native/IDataTransferManagerInterOp.cs

@@ -0,0 +1,57 @@
+/*
+ * Greenshot - a free and open source screenshot tool
+ * Copyright (C) 2007-2015 Thomas Braun, Jens Klingen, Robin Krom
+ * 
+ * For more information see: http://getgreenshot.org/
+ * The Greenshot project is hosted on Sourceforge: http://sourceforge.net/projects/greenshot/
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 1 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+using System;
+using System.Runtime.InteropServices;
+using Windows.ApplicationModel.DataTransfer;
+
+namespace GreenshotWin10Plugin.Native
+{
+	/// <summary>
+	/// The IDataTransferManagerInterOp is documented here: https://msdn.microsoft.com/en-us/library/windows/desktop/jj542488(v=vs.85).aspx.
+	/// This interface allows an app to tie the share context to a specific
+	/// window using a window handle. Useful for Win32 apps.
+	/// </summary>
+	[ComImport, Guid("3A3DCD6C-3EAB-43DC-BCDE-45671CE800C8")]
+	[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
+	public interface IDataTransferManagerInterOp
+	{
+		/// <summary>
+		/// Get an instance of Windows.ApplicationModel.DataTransfer.DataTransferManager
+		/// for the window identified by a window handle
+		/// </summary>
+		/// <param name="appWindow">The window handle</param>
+		/// <param name="riid">ID of the DataTransferManager interface</param>
+		/// <param name="pDataTransferManager">The DataTransferManager instance for this window handle</param>
+		/// <returns>HRESULT</returns>
+		[PreserveSig]
+		uint GetForWindow([In] IntPtr appWindow, [In] ref Guid riid, [Out] out DataTransferManager pDataTransferManager);
+
+		/// <summary>
+		/// Show the share flyout for the window identified by a window handle
+		/// </summary>
+		/// <param name="appWindow">The window handle</param>
+		/// <returns>HRESULT</returns>
+		[PreserveSig]
+		uint ShowShareUIForWindow(IntPtr appWindow);
+	}
+
+}