ENH: New format for warning and error messages

- Add cmMakefile methods IssueError and IssueWarning
  - Maintain an explicit call stack in cmMakefile
  - Include context/call-stack info in messages
  - Nested errors now unwind the call stack
  - Use new mechanism for policy warnings and errors
  - Improve policy error message
  - Include cmExecutionStatus pointer in call stack
    so that errors deeper in the C++ stack under
    a command invocation will become errors for the
    command

Source/cmListFileCache.h

@@ -50,14 +50,18 @@ struct cmListFileArgument
   long Line;
 };
 
-struct cmListFileFunction
+struct cmListFileContext
 {
   std::string Name;
-  std::vector<cmListFileArgument> Arguments;
   std::string FilePath;
   long Line;
 };
 
+struct cmListFileFunction: public cmListFileContext
+{
+  std::vector<cmListFileArgument> Arguments;
+};
+
 struct cmListFile
 {
   cmListFile()