bottle: allow --keep-old to ignore same sha256s.
bottle: allow --keep-old to ignore same sha256s.

It should refuse to change existing ones but it should allow them to be
the same and silently ignore.

konqui/brew,gregory-nisbet/brew,jmsundar/brew,MikeMcQuaid/brew,reitermarkus/brew,claui/brew,mgrimes/brew,hanxue/linuxbrew,sjackman/homebrew,amar-laksh/brew_sudo,palxex/brew,maxim-belkin/brew,EricFromCanada/brew,MikeMcQuaid/brew,muellermartin/dist,gregory-nisbet/brew,bfontaine/brew,DomT4/brew,palxex/brew,vitorgalvao/brew,reitermarkus/brew,nandub/brew,rwhogg/brew,JCount/brew,Homebrew/brew,toonetown/homebrew,nandub/brew,nandub/brew,alyssais/brew,EricFromCanada/brew,toonetown/homebrew,mgrimes/brew,ilovezfs/brew,jmsundar/brew,toonetown/homebrew,pseudocody/brew,JCount/brew,EricFromCanada/brew,Linuxbrew/brew,reitermarkus/brew,JCount/brew,aw1621107/brew,nandub/brew,zmwangx/brew,vitorgalvao/brew,amar-laksh/brew_sudo,konqui/brew,alyssais/brew,EricFromCanada/brew,mahori/brew,muellermartin/dist,claui/brew,aw1621107/brew,maxim-belkin/brew,amar-laksh/brew_sudo,reelsense/brew,konqui/brew,Homebrew/brew,zmwangx/brew,tonyg/homebrew,tonyg/homebrew,alyssais/brew,JCount/brew,Homebrew/brew,pseudocody/brew,maxim-belkin/brew,ilovezfs/brew,mgrimes/brew,DomT4/brew,reitermarkus/brew,claui/brew,konqui/brew,hanxue/linuxbrew,mahori/brew,hanxue/linuxbrew,tonyg/homebrew,MikeMcQuaid/brew,Linuxbrew/brew,mahori/brew,palxex/brew,rwhogg/brew,MikeMcQuaid/brew,DomT4/brew,zmwangx/brew,reelsense/brew,pseudocody/brew,Linuxbrew/brew,claui/brew,DomT4/brew,bfontaine/brew,sjackman/homebrew,Homebrew/brew,rwhogg/brew,muellermartin/dist,bfontaine/brew,vitorgalvao/brew,ilovezfs/brew,reelsense/brew,vitorgalvao/brew,sjackman/homebrew,gregory-nisbet/brew,sjackman/homebrew,aw1621107/brew,jmsundar/brew,Linuxbrew/brew,mahori/brew