Replace begin+while with loop+break (preferred)

matz: http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-core/6745
stackoverflow: http://stackoverflow.com/questions/136793/is-there-a-do-while-loop-in-ruby
opal issue: http://github.com/opal/opal/issues/575#issuecomment-53940329