hw: destruct scheduling contexts

ref #589

base-hw/src/core/kernel/scheduler.h

@@ -138,6 +138,13 @@ class Kernel::Double_list<T>::Item
 		 * Constructor
 		 */
 		Item() : _next(0), _prev(0), _list(0) { }
+
+
+		/***************
+		 ** Accessors **
+		 ***************/
+
+		Double_list<T> * list() { return _list; }
 };
 
 template <typename T>

base-hw/src/core/kernel/thread.h

@@ -72,6 +72,14 @@ class Kernel::Execution_context : public Cpu_scheduler::Item
 		 * Continue execution
 		 */
 		virtual void proceed() = 0;
+
+		/**
+		 * Destructor
+		 */
+		virtual ~Execution_context()
+		{
+			if (list()) { cpu_scheduler()->remove(this); }
+		}
 };
 
 class Kernel::Thread