Fixed non-iso8601 Tuesday/Thursday dates

Oddly this bug only appeared in Firefox (25) and IE (10) while remaining hidden in Chrome (30).

$.timeago("Tue Nov 12 20:45:30 2013")

Chrome: "about 13 hours ago"
Firefox/IE: "NaN years ago"

Now you might say you don't like people shoving non-iso8601 into your api, but at the time I wrote my site I had no idea that `new Date(strange_timestamp)` solved my conversion problem. I just pushed my ugly timestamp into timeago and thought it worked. So either you actually intercept and fail on bad timestamps or do this minor error avoidance tactic.