manage interpreter instance in interpreter object Currently it is only possible to have one application or interpreter object. Enforce that restriction. * octave.h, octave.cc (application::the_interpreter): Delete. (application::application): Ensure only one application is created at once. * interpreter.cc, interpreter.h (interpreter::instance): New static variable. (interpreter::interpreter): Ensure only one is created at once. (interpreter::~interpreter): Set instance to nullptr. (interpreter::the_interpreter): New function. * interpreter-private.cc, interpreter-private.cc (__get_interpreter__): Delete. Replace all uses with octave::interpreter::the_interpreter.

--- a/libinterp/corefcn/interpreter-private.h	Wed May 17 22:13:28 2017 -0700
+++ b/libinterp/corefcn/interpreter-private.h	Thu May 18 10:53:24 2017 -0400
@@ -27,12 +27,9 @@
 
 #include <string>
 
-#include "interpreter.h"
-
 namespace octave
 {
-  // Expect these functions to change without warning.
-  extern interpreter& __get_interpreter__ (const std::string& who);
+  class load_path;
 
   extern load_path& __get_load_path__ (const std::string& who);
 }