util.smqueue: Minor reformatting for code style, add some comments The `smqueue` table (of methods) is no longer exported, as I couldn't see it being used anywhere and it is unconventional (only new() is exported, and methods should be called on the objects returned from that).

local xpcall = xpcall;

if select(2, xpcall(function (x) return x end, function () end,  "test")) ~= "test" then
	xpcall = require"prosody.util.compat".xpcall;
end

return {
	xpcall = xpcall;
};