COMP: Fix nested class member access

Nested classes have no special access to other members of their
enclosing class.  In cmFileCopier the nested class MatchRule must use
MatchProperties, so we grant friendship to it.

Source/cmFileCommand.cxx

@@ -947,6 +947,8 @@ protected:
     mode_t Permissions;
     MatchProperties(): Exclude(false), Permissions(0) {}
   };
+  struct MatchRule;
+  friend struct MatchRule;
   struct MatchRule
   {
     cmsys::RegularExpression Regex;