Fix for ticket 1282

[victor-homyakov]

Attempt to fix https://prototype.lighthouseapp.com/projects/8886/tickets/1282-latest-prototypejs-from-github-repo-fails-in-opera

Opera (at least 11.X) has false positive result in feature test 'styleFloat' in DIV.style, but should have its own getStyle_Opera and standard setOpacity/getOpacity.

Another variant:

  if (Prototype.Browser.Opera) {
    // Opera also has 'styleFloat' in DIV.style
    methods.getStyle = getStyle_Opera;
  } else if ('styleFloat' in DIV.style) {
    methods.getStyle = getStyle_IE;
  }
  if (!STANDARD_CSS_OPACITY_SUPPORTED) {
    methods.setOpacity = setOpacity_IE;
    methods.getOpacity = getOpacity_IE;
  }