Update issue #76 : MRU file list clears document before loading file. 
Dropping files clears graph unless control key is held down when file is dropped.
Dropping file on filter shows error if filter does not support IFileSourceFilter or IFileSinkFilter


git-svn-id: http://graph-studio-next.googlecode.com/svn/trunk@175 c2f33eb2-41b2-391d-4cb4-d9d0608729ba