Residential mortgage-backed securities (RMBS) are back with a vengeance. These financial instruments, used by financial institutions to raise their own debt from bond markets against the value of bundles of home loans, spent a period in purgatory after they were widely seen as having facilitated the contagion of the US subprime lending crisis into the global financial system from 2007. (Do the names Fannie Mae and Freddie Mac ring any bells?) They have since regained favour in markets such as the US and the UK and, more recently, in Ireland. As I previously reported, Goldman Sachs was among the first…