Removed support for directly mocking a protected member function

Taking a function pointer on a base member protected function is actually invalid.
This could work with a pointer on the derived class member function, that is &derived::method instead of &base::method however there is no way to pass the derived class from MOCK_BASE_CLASS to the mock::detail::base helper if template classes are to be supported.

Anyway the now documented workaround is simple enough and the same as for private member functions.

As a side note the changes from ed36823235 might not be needed any more…

test/test_mock.cpp

@@ -364,7 +364,7 @@ namespace
     {
         virtual ~base()
         {}
-    protected:
+
         virtual void m1() = 0;
     };
 
@@ -413,7 +413,7 @@ namespace
     {
         virtual ~base()
         {}
-    protected:
+
         virtual void m1() = 0;
     };
 
@@ -444,7 +444,6 @@ namespace stdcall
         virtual ~base()
         {}
 
-    protected:
         virtual void MOCK_STDCALL m1() = 0;
     };