util.human.io: Prefer using the $COLUMNS environment variable if set (by readline)

Feels like it should be faster.

util/human/io.lua

@@ -109,6 +109,8 @@ if utf8.len and utf8.offset then
 end
 
 local function term_width(default)
+	local env_cols = os.getenv "COLUMNS";
+	if env_cols then return env_cols; end
 	local stty = io.popen("stty -a");
 	if not stty then return default; end
 	local result = stty:read("*a");

util/prosodyctl/shell.lua

@@ -30,7 +30,7 @@ local function read_line(prompt_string)
 end
 
 local function send_line(client, line)
-	client.send(st.stanza("repl-input", { width = os.getenv "COLUMNS" or term_width() }):text(line));
+	client.send(st.stanza("repl-input", { width = term_width() }):text(line));
 end
 
 local function repl(client)