VS11: Allow using folders with the VS11 Express Edition (#13770)

Solution folders are supported as read-only in the VS11 Express
Edition, so do not prohibit their use just because we detect the
express edition (as we did in the VS10 generator).

Inspired-by: Paris

Source/cmGlobalGenerator.cxx

@@ -2047,7 +2047,7 @@ bool cmGlobalGenerator::UseFolderProperty()
     }
 
   // By default, this feature is OFF, since it is not supported in the
-  // Visual Studio Express editions:
+  // Visual Studio Express editions until VS11:
   //
   return false;
 }

Source/cmGlobalVisualStudio11Generator.cxx

@@ -93,3 +93,12 @@ cmLocalGenerator *cmGlobalVisualStudio11Generator::CreateLocalGenerator()
   lg->SetGlobalGenerator(this);
   return lg;
 }
+
+//----------------------------------------------------------------------------
+bool cmGlobalVisualStudio11Generator::UseFolderProperty()
+{
+  // Intentionally skip over the parent class implementation and call the
+  // grand-parent class's implementation. Folders are not supported by the
+  // Express editions in VS10 and earlier, but they are in VS11 Express.
+  return cmGlobalVisualStudio8Generator::UseFolderProperty();
+}

Source/cmGlobalVisualStudio11Generator.h

@@ -33,6 +33,7 @@ public:
   virtual std::string GetUserMacrosDirectory() { return ""; }
 protected:
   virtual const char* GetIDEVersion() { return "11.0"; }
+  bool UseFolderProperty();
 private:
   class Factory;
 };