Fix Jim interpreter memory leak

Change-Id: I71d7d97e7dc315c42fc43b65cb5fcecd7bdfb581
Signed-off-by: Marc Schink <openocd-dev@marcschink.de>
Reviewed-on: http://openocd.zylin.com/2959
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>

src/helper/command.h

@@ -307,6 +307,14 @@ struct command_context *current_command_context(Jim_Interp *interp);
  * creates a command interpreter.
  */
 struct command_context *command_init(const char *startup_tcl, Jim_Interp *interp);
+/**
+ * Shutdown a command context.
+ *
+ * Free the command context and the associated Jim interpreter.
+ *
+ * @param context The command_context that will be destroyed.
+ */
+void command_exit(struct command_context *context);
 /**
  * Creates a copy of an existing command context.  This does not create
  * a deep copy of the command list, so modifications in one context will