DOC: Improve MINC transform adapter exception message

Improve MINC transform adapter exception message:
- Make it more neutral.
- Respect the MINC library case: use uppercases.
- Use "D" (uppercase) instead of "d" (lowercase) to mean "-dimension".
- Do not use "xfm" to refer to "transform" for the sake of clearliness.

Author: jhlegarreta

Modules/IO/TransformMINC/include/itkMINCTransformAdapter.h

@@ -293,7 +293,7 @@ class ITK_TEMPLATE_EXPORT MINCTransformAdapter
   {
     if (VInputDimension != 3 || VOutputDimension != 3)
     {
-      itkExceptionMacro("Sorry, only 3D to 3d minc xfm transform is currently implemented");
+      itkExceptionMacro("MINC transform is currently implemented only for 3D to 3D.");
     }
   }