Two small GUI bug fixes

[Wolfgang Lux]

Hello,

here are two more small bug fixes for GUI.

The first concerns NSTableView's -draggingUpdated: implementation, which
invariably passes NSTableViewDropAbove instead of the current drop  
operation
to the delegate's - 
tableView:validateDrop:proposedRow:proposedDropOperation:
method.

NSTableView.patch
Description: Binary data

The second patch fixes NSDocument's -windowForSheet: operation to return
nil instead of [NSApp mainWindow] if the document has no associated  
window.
This is the behavior implemented by Cocoa on OS X (the documentation  
does
say otherwise). It is also the only reasonable behavior, it would not  
make
sense to attach a sheet to window that is not owned by the document.

NSDocument.patch
Description: Binary data

Wolfgang