MUC: Add basic "GC3" participant (affiliation) list fetch RSM version currently held back until a planned restructuring of how we store affiliations in MUC. This is because RSM needs a stable ordered list, which we don't currently have.

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;
};