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/test.h

@@ -0,0 +1,7 @@
+#ifndef __TEST_H__
+#define __TEST_H__
+
+
+int mm0_test_global_vm_integrity(void);
+
+#endif /* __TEST_H__ */