Drop unique constraint and make sure we allow NULLs before doing username migration (bug 1131717)
Drop unique constraint and make sure we allow NULLs before doing username migration (bug 1131717)

ingenioustechie/zamboni,jasonthomas/zamboni,jasonthomas/zamboni,diox/zamboni,kumar303/zamboni,ingenioustechie/zamboni,eviljeff/zamboni,ddurst/zamboni,ddurst/zamboni,ayushagrawal288/zamboni,tsl143/zamboni,mstriemer/zamboni,clouserw/zamboni,ayushagrawal288/zamboni,ddurst/zamboni,ddurst/zamboni,clouserw/zamboni,jamesthechamp/zamboni,mozilla/zamboni,Hitechverma/zamboni,mozilla/zamboni,Jobava/zamboni,shahbaz17/zamboni,eviljeff/zamboni,jasonthomas/zamboni,ingenioustechie/zamboni,tsl143/zamboni,diox/zamboni,kumar303/zamboni,ayushagrawal288/zamboni,ingenioustechie/zamboni,shahbaz17/zamboni,elysium001/zamboni,mstriemer/zamboni,Hitechverma/zamboni,jamesthechamp/zamboni,clouserw/zamboni,shahbaz17/zamboni,shahbaz17/zamboni,luckylavish/zamboni,elysium001/zamboni,Hitechverma/zamboni,jamesthechamp/zamboni,washort/zamboni,tsl143/zamboni,mudithkr/zamboni,mudithkr/zamboni,mudithkr/zamboni,luckylavish/zamboni,clouserw/zamboni,tsl143/zamboni,diox/zamboni,luckylavish/zamboni,kumar303/zamboni,elysium001/zamboni,eviljeff/zamboni,Hitechverma/zamboni,mozilla/zamboni,kumar303/zamboni,jasonthomas/zamboni,ayushagrawal288/zamboni,diox/zamboni,eviljeff/zamboni,mudithkr/zamboni,washort/zamboni,mozilla/zamboni,washort/zamboni,Jobava/zamboni,Jobava/zamboni,luckylavish/zamboni,mstriemer/zamboni,elysium001/zamboni,Jobava/zamboni,jamesthechamp/zamboni,mstriemer/zamboni,washort/zamboni