Push footer to bottom of browser on short pages

This has been bugging me forever.  So now it's...

from this:
![screenshot 2014-05-21 16 58 59](https://cloud.githubusercontent.com/assets/2205926/3048914/9b9dc098-e151-11e3-94ea-55ef822f5e7b.png)

to this:
![screenshot 2014-05-21 18 20 48](https://cloud.githubusercontent.com/assets/2205926/3048913/9b9d5c48-e151-11e3-83b1-3f59c7637c69.png)

tested for real in modern chrome, firefox, safari, and in browserstack for ie9, iphone and ipad... both level pages and short pages (e.g. /join).