Implement some library procedures for the Java back end.

Estimated hours taken: 5
Branches: main

Implement some library procedures for the Java back end.

library/std_util.m:
	Defined the type mutvar(T) as an array of java.lang.Objects (which
	will always be size 1)

	Implemented the following procedures in Java:
		get_registers/3
		check_for_floundering/1
		discard_trail_ticket/0
		swap_heap_and_solutions_heap/0
		partial_deep_copy/3
		reset_solutions_heap/1
		new_mutvar/2
		get_mutvar/2
		set_mutvar/2

java/runtime/VA_PseudoTypeInfo_Struct0.java:
	This new file is a workaround which allows std_util.m to successfully
	compile in grade Java.

java/runtime/VA_PseudoTypeInfo_Struct0.java

@@ -0,0 +1,16 @@
+//
+// Copyright (C) 2001-2004 The University of Melbourne.
+// This file may only be copied under the terms of the GNU Library General
+// Public License - see the file COPYING.LIB in the Mercury distribution.
+//
+
+package mercury.runtime;
+
+public class VA_PseudoTypeInfo_Struct0 extends PseudoTypeInfo {
+	public VA_PseudoTypeInfo_Struct0(
+			TypeCtorInfo_Struct type_ctor_info,
+			int arity,
+			Object[] args) {
+		// XXX stub only
+	}
+}