Clarify notation of MS-SBVAR
Section 4.18 of the manual refers to variables limke A^0, A^+ or Q. But they seem to come from a different paper than the cited Sims/Waggoner/Zha (2008). My guess is Sims/Zha (1998). See also http://www.dynare.org/phpBB3/viewtopic.php?f=1&t=6801&p=19671#p19671