Detect the use of incompatible flags for wxGridSizer too.

Complain if wxEXPAND is combined with both horizontal and vertical alignment
flags, as this doesn't make sense and, moreover, the behaviour has changed
since the last commit: now wxEXPAND is ignored instead of overriding the
alignment flags if they are combined.

tests/sizers/gridsizer.cpp

@@ -39,9 +39,11 @@ public:
 private:
     CPPUNIT_TEST_SUITE( GridSizerTestCase );
         CPPUNIT_TEST( Expand );
+        CPPUNIT_TEST( IncompatibleFlags );
     CPPUNIT_TEST_SUITE_END();
 
     void Expand();
+    void IncompatibleFlags();
 
     // Clear the current sizer contents and add the specified windows to it,
     // using the same flags for all of them.
@@ -156,3 +158,12 @@ void GridSizerTestCase::Expand()
     CPPUNIT_ASSERT_EQUAL( wxSize(sizeChild.x, sizeRest.y),
                           children[3]->GetSize() );
 }
+
+void GridSizerTestCase::IncompatibleFlags()
+{
+    WX_ASSERT_FAILS_WITH_ASSERT_MESSAGE
+    (
+        "Combining wxEXPAND and wxCENTRE should assert",
+        m_sizer->Add(10, 10, wxSizerFlags().Expand().Centre())
+    );
+}