[SHELL32]

* Add support for the CF_HDROP format in the shell drop targets.
* Implement IAsyncOperation for the shell data object implementation, which is how one checks to see if it's safe to perform a background copy.
* Actually check for the IAsyncOperation interface in the drop targets.
* 7-zip and WinRAR are now mostly working correctly in terms of drag and drop.
* Brought to you by Huw Campbell.
CORE-3760

svn path=/trunk/; revision=61576