Bugfixes, enhancements

- Fixed an important bug with shadow object handling.
  When a shadow is dropped, if there are references left
  to it, both the object in front and dropped object becomes
  a shadow of the original object underneath. We had thought
  of this case but had not increase the shadow count.

- Added a test mechanism that tests the number of objects,
  vmfiles, shadows etc. by first counting them and trying to
  reach the same number by other means, i.e. per-object-shadow counts.
  It discovered a plethora of bugs.

- Added new set of functions to register objects, files and tasks
  globally with the pager, these functions introduce a refcount as
  well as adding structures to linked lists.

- fork/exit now seems to work stably i.e. no negative shadow counts etc.

tasks/mm0/include/globals.h

@@ -0,0 +1,13 @@
+#ifndef __GLOBALS_H__
+#define __GLOBALS_H__
+
+struct global_list {
+	int total;
+	struct list_head list;
+};
+
+extern struct global_list global_vm_files;
+extern struct global_list global_vm_objects;
+extern struct global_list global_tasks;
+
+#endif /* __GLOBALS_H__ */