darwin: Fix uiTable checkbox value not calling SetCellValue().

The SetCellValue() when clicking a checkbox within a uiTable is
never called. The UI happiliy updates suggesting the value has
been set - which is not actually the case.

The checkbox not redrawing with the actual check box value from
the model is another related issue, see andlabs#507.

darwin/tablecolumn.m

@@ -181,6 +181,8 @@ - (id)initWithFrame:(NSRect)r params:(struct textColumnCreateParams *)p
 			[self->cb setTransparent:NO];
 			uiDarwinSetControlFont(self->cb, NSRegularControlSize);
 			[self->cb setTranslatesAutoresizingMaskIntoConstraints:NO];
+			[self->cb setTarget:self];
+			[self->cb setAction:@selector(uiprivOnCheckboxAction:)];
 			[self addSubview:self->cb];
 
 			if (self->tf != nil) {