Fix BALMLayout archiving issues.

SharedSolver was archiving too many constraints, partly because of
multiple typos, also because it archived some which were just artifacts
of the layout process. These extra constraints are created when the
layout calls SetRange() on the left/top/right/bottom tabs during layout.

* LinearSpec/ActiveSetSolver had to be adjusted to get access to the
  constraints added by the SetRange() calls.
* BALM::TabBase was adjusted to avoid a segfault during unarchiving,
  caused by an unitialized member.
* ALMFriendLayoutTest was adjusted to include a more obvious custom
  constraint for testing.

headers/libs/linprog/LinearSpec.h

@@ -58,6 +58,10 @@ public:
 	virtual	ResultType			FindMins(const VariableList* variables) = 0;
 	virtual	ResultType			FindMaxs(const VariableList* variables) = 0;
 
+	virtual	void				GetRangeConstraints(const Variable* var,
+									const Constraint** _min,
+									const Constraint** _max) const = 0;
+
 protected:
 			LinearSpec*			fLinearSpec; 
 };
@@ -138,6 +142,9 @@ public:
 
 			BString				ToString() const;
 
+			void				GetRangeConstraints(const Variable*,
+									const Constraint** _min,
+								   	const Constraint** _max) const;
 	const	ConstraintList&		Constraints() const;
 	const	VariableList&		UsedVariables() const;
 	const	VariableList&		AllVariables() const;