Force Safari 7 to open link in the current tab
As far as I know, there's no way to force a link to open in the current tab when it has target="_blank". There's controversy over this attribute in the web development world because it's considered overbearing to force a user to open a link in a new tab when they don't want to.

Essentially, the browser is seen as the user's property, and they have the right to decide where they want links to open. This link property has been abused many times for popup ads and, while it can be useful, it generally creates a bad user experience.

I assume the only way around it would be to create (or find?) an extension that goes through all of the links on a page and removes the target attribute. It appears that @sayzlim has found one for you (see here).

As for your third example, there's no way around that other than to disable JavaScript in your browser.