Suppress Warnings: instance variable @installed_by_version not initialized

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43551 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
Suppress warnings: File.exists? is a deprecated name

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43552 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
Suppress warnings: ambiguous first argument; put parentheses or even spaces

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43553 b2dd03c8-39d4-4d8f-98ff-823fe69b080e