Don't destructively include pullquotes in the loop

When pullquotes are set to display in a waterfall, pullquotes were added regardless of the type of waterfall - which was causing them (and posts of the `post` post type) to be displayed on archive pages where they didn't belong.

This changeset ensures that pullquotes are only added to loops where A) `post_type` isn't specified or B) where the `post` post type appears in the `post_type` array.
Merge pull request #19 from borkweb/6272-post-type-waterfalls

Don't destructively include pullquotes in the loop
Merge branch 'master' of github.com:GigaOM/go-quotes into 6211-wrong-quote

Conflicts:
	components/class-go-quotes.php