Fixed a bug in SimRef.__repr__.
Fixed a bug in SimRef.__repr__.

axt/angr,chubbymaggie/simuvex,f-prettyland/angr,chubbymaggie/simuvex,axt/angr,iamahuman/angr,chubbymaggie/angr,axt/angr,tyb0807/angr,angr/angr,tyb0807/angr,f-prettyland/angr,schieb/angr,angr/simuvex,angr/angr,iamahuman/angr,schieb/angr,schieb/angr,chubbymaggie/angr,chubbymaggie/angr,tyb0807/angr,f-prettyland/angr,iamahuman/angr,zhuyue1314/simuvex,chubbymaggie/simuvex,angr/angr