Better fix for 32 bit wxOSX build

Instead of disabling vertical alignment support in wxDataViewCtrl, move the
private variables to the header file: this is supported by all versions of the
Objective-C runtime, including the old one used for 32 bit applications,
unlike the new way based on declaring the variable in an anonymous extension.

This replaces the changes of 22216b70e7.

include/wx/osx/cocoa/dataview.h

@@ -376,6 +376,12 @@ private:
     #define wxTextFieldCell NSTextFieldCell
 #else
 @interface wxTextFieldCell : NSTextFieldCell
+{
+@private
+    int _wxAlignment;
+    BOOL _adjustRect;
+}
+
     -(void) setWXAlignment:(int)alignment;
 @end
 #endif