Fix autoreply email address for site contact form.

#4920

This PR addresses https://github.com/openscholar/openscholar/issues/4920#issuecomment-37650774.
Now the auto-reply is sent correctly (to the original sender of the form. Not the site owner):

![selection_018](https://f.cloud.github.com/assets/4497748/2457386/70774bda-af35-11e3-9131-d4e5b41b6264.png)