STYLE: Explicitly declare virtual for derived class member functions

Class member functions derived from parent class with virtual functions
of the same name are implicitly virtual.  This patch set uses a macro
for the c++11 override keyword to indicate that this function was
intended to be overridden in this derived class.

Ensuring that functions signatures are described as virtual is not
strictly needed, but it facilitates maintenance by being consistent.
Approximately 1/2 of the toolkit had the explicit virtual designation and 1/2
relied on implicit behavior.

The ITK_OVERRIDE define allows for non-c++11 compilers to continue to work.

Change-Id: Iba5c2970f2bad4f7f664b92a4420d217546bb22f

Author: hjmjohnson

Modules/Core/Common/include/itkMacro.h

@@ -118,6 +118,16 @@ namespace itk
   #endif
 #endif
 
+// In c++11 the override keyword allows you to explicity define that a function
+// is intended to override the base-class version.  This makes the code more
+// managable and fixes a set of common hard-to-find bugs.
+#if __cplusplus >= 201103L
+#define ITK_OVERRIDE override
+#else
+#define ITK_OVERRIDE
+#endif
+
+
 /** Define two object creation methods.  The first method, New(),
  * creates an object from a class, potentially deferring to a factory.
  * The second method, CreateAnother(), creates an object from an
@@ -156,7 +166,7 @@ namespace itk
     }
 
 #define itkCreateAnotherMacro(x)                               \
-  virtual::itk::LightObject::Pointer CreateAnother(void) const \
+  virtual::itk::LightObject::Pointer CreateAnother(void) const ITK_OVERRIDE \
     {                                                          \
     ::itk::LightObject::Pointer smartPtr;                      \
     smartPtr = x::New().GetPointer();                          \
@@ -196,7 +206,7 @@ namespace itk
     rawPtr->UnRegister();                                      \
     return smartPtr;                                           \
     }                                                          \
-  virtual::itk::LightObject::Pointer CreateAnother(void) const \
+  virtual::itk::LightObject::Pointer CreateAnother(void) const ITK_OVERRIDE \
     {                                                          \
     ::itk::LightObject::Pointer smartPtr;                      \
     smartPtr = x::New().GetPointer();                          \

Modules/Core/Common/include/itkObject.h

@@ -71,7 +71,7 @@ class ITKCommon_EXPORT Object:public LightObject
    * object that is exactly the same type as the referring object.
    * This is useful in cases where an object has been cast back to a
    * base class. */
-  virtual LightObject::Pointer CreateAnother() const;
+  virtual LightObject::Pointer CreateAnother() const ITK_OVERRIDE;
 
   /** Standard part of all itk objects. */
   itkTypeMacro(Object, LightObject);