Redo tpls using ideas from Drupal 7

With the tpl refresh that I’m helping with in Drupal 7, it would be good to get those ideas ported into Zen 6.x-2.x.

I don't like making changes to the HTML in tpl files after a release is stable. So adding those changes into Zen 6.x-1.x would be kind of mean to people using it.

Issue queues can be a poor window into big picture ideas, but this issue will link to the specific issues for this idea as they are created.

page.tpl.php:
#622324: Update page.tpl to use ideas from D7
#375953: Change sidebar names to be RTL friendly (might change this depending on core's #226587: Default sidebar region labels are confusing (wrong) for RTL languages)
#362477: Add missing RTL support for IE conditional stylesheets
#445790: Move search box to header
#445814: Change primary/secondary link rendering and move secondary menu to footer
#445822: Simplify wrapper divs around logo, site name, slogan
#445830: Rename clear-block CSS class to clearfix
#621798: Change sidebar variables to be RTL friendly and $shows_blocks compatible
#308376: Add page navigation links by expanding "skip to nav" idea
#308254: Make "skip to nav" styling more useful and less intrusive

#547696: Update node.tpl to use ideas from D7
#620794: Update block.tpl to use ideas from D7
#548994: Update comment.tpl and comment-wrapper.tpl to use ideas from D7