Readline: make M-Enter insert a newline

Before, it was only possible with C-v C-j but it's too useful
to require such an awkward method.

There is a precedent in, e.g., zsh and fish for the new binding.

json-rpc-shell.c

@@ -246,11 +246,23 @@ input_rl_on_run_editor (int count, int key)
 	return 0;
 }
 
+static int
+input_rl_newline_insert (int count, int key)
+{
+	(void) count;
+	(void) key;
+
+	rl_insert_text ("\n");
+	return 0;
+}
+
 static int
 input_rl_on_startup (void)
 {
 	rl_add_defun ("run-editor", input_rl_on_run_editor, -1);
 	rl_bind_keyseq ("\\ee", rl_named_function ("run-editor"));
+	rl_add_defun ("newline-insert", input_rl_newline_insert, -1);
+	rl_bind_keyseq ("\\e\\r", rl_named_function ("newline-insert"));
 	return 0;
 }
 
@@ -268,6 +280,7 @@ input_rl_start (struct input *input, const char *program_name)
 	rl_readline_name = slash ? ++slash : program_name;
 	rl_startup_hook = input_rl_on_startup;
 	rl_catch_sigwinch = false;
+	rl_change_environment = false;
 
 	hard_assert (self->prompt != NULL);
 	rl_callback_handler_install (self->prompt, input_rl_on_input);
@@ -360,16 +373,14 @@ input_rl_set_prompt (struct input *input, char *prompt)
 	free (self->prompt);
 	self->prompt = prompt;
 
-	if (!self->active)
+	if (!self->active || self->prompt_shown <= 0)
 		return;
 
 	// First reset the prompt to work around a bug in readline
 	rl_set_prompt ("");
-	if (self->prompt_shown > 0)
 	rl_redisplay ();
 
 	rl_set_prompt (self->prompt);
-	if (self->prompt_shown > 0)
 	rl_redisplay ();
 }
 
@@ -2716,6 +2727,7 @@ static void
 resume_terminal (struct app_context *ctx)
 {
 	ctx->input->vtable->prepare (ctx->input, true);
+	ctx->input->vtable->on_terminal_resized (ctx->input);
 	ev_io_start (EV_DEFAULT_ &ctx->tty_watcher);
 	ctx->input->vtable->show (ctx->input);
 }