Add support for aborting invocations; fixed my commit from Friday, so it doesn't...

Add support for aborting invocations; fixed my commit from Friday, so it doesn't break compatibility.
2010-03-05  Martin Baulig  <martin@ximian.com>

	Add support for aborting invocations.

	* IInvokeAsyncResult.cs: New file.
	(IInvokeAsyncResult): New public interface; derives from
	`IAsyncResult' and contains an Abort() method.

	* Connection.cs
	(Connection.VM_BeginInvokeMethod): Return the `id'.
	(Connection.VM_AbortInvoke): New method.

	* ObjectMirror.cs
	(ObjectMirror.AbortInvoke): New internal static method.

svn path=/trunk/mcs/; revision=153336