set-cursor in window<%>
Sets the window's cursor. Providing #f instead of a cursor
value removes the window's cursor.
If a window does not have a cursor, it uses the cursor of its parent. Frames and dialogs start with the standard arrow cursor, and text fields start with an I-beam cursor. All other windows are created without a cursor.
( -> void
send a-window set-cursor cursor)
cursor : cursor% object or #f