Update jQuery requirements in resources/startup.js per jQuery 1.7.x release

Update jQuery requirements in resources/startup.js per jQuery 1.7.x release

- Check http://jquery.com/:
 * IE 6.0+, FF 3.6+, Safari 5.0+, Opera, Chrome

- It does not include an Opera number, but they are only
  actively testing for Opera 11.x versions. Also Operate
  is quite bold in their upgrade requirement in-browser,
  so that shouldn't be much of an issue.

  I've also updated
  https://www.mediawiki.org/wiki/Compatibility#Browser

  Note that this means that we no longer support enhanced functionality in
  some browsers that are currently still above the 0.1% wmf-traffic threshold
  we keep. I've therefor split [[mw:Compatibility#Browser]] in a "Grade A"
  and "Grade B" section. One that we support for all functionality, and the
  others we support because of traffic, but not "everything" will work.
  Right now the only notable difference will be jQuery and depending modules.

  In reality Grade B will still get the same data served as Grade A, since
  startup.js only enforces IE6 right now (bug 35906)

  Auto-updating Chrome will not need a check, and Chrome < 1.0 is very minor,
  and will probably even work just fine.

Change-Id: If60de580fc892ced1a43a0bc4958988d98d087d9