Show excerpt enabled content only on index page

If the page is an index page and there is an excerpt in the post then
don't display the full article. Only until the excerpt.

Reference: http://octopress.org/docs/blogging/
Merge branch 'master' of github.com:creativepsyco/calm-shallow-sea

* 'master' of github.com:creativepsyco/calm-shallow-sea:
  Fix for errors during rake generate. According to this Stack Overflow question: http://stackoverflow.com/q/17976140/ must rename the partials with underscore to prevent automatic compilation