Various little fixes here and there:
Various little fixes here and there: - Basic support for dragging the selection is in (still does not do anything, will do the action binding later). - Fixes to the cell-selection-code-when-you-type-a-formula code - ExprTrees are now properly refcounted (instead of only refcounting the root node). This is required for the Paste special/with-arithmetic operation feature. - Expression decoding (for pasting a formula with relative references) now takes into account operator precedence to avoid cluttering the pasted expression with extra paretheses. Other smallish fixes which I forget now. Miguel.