Merge remote-tracking branch 'origin/topic/awelzel/2285-assert-statement'

* origin/topic/awelzel/2285-assert-statement:
  NEWS: Small section about assert statement
  Stmt: Rework assertion hooks break semantics
  Stmt: Introduce assert statement and related hooks
  ZeekArgs: Helper for empty arguments
  Reporter: Allow AssertStmt to throw InterpreterException
  Lift backtrace() code into Func.{h,cc}

src/script_opt/Stmt.cc

@@ -919,6 +919,11 @@ StmtPtr InitStmt::DoReduce(Reducer* c)
 	return ThisPtr();
 	}
 
+StmtPtr AssertStmt::Duplicate()
+	{
+	return SetSucc(new AssertStmt(cond->Duplicate(), msg ? msg->Duplicate() : nullptr));
+	}
+
 StmtPtr WhenStmt::Duplicate()
 	{
 	FuncType::CaptureList* cl_dup = nullptr;