Add common passwords from xato.net

Mark Burnett publishes lists of top passwords occasionally. This PR adds
the top 500 and top 1024 passwords, as of 2011-06-20, linked from this
blog post:

http://xato.net/passwords/more-top-worst-passwords/

He also does a fair bit of frequency analysis there.

The 1024 list, should probably used instead of the original
unix_password.txt file. unix_password.txt  was added on 2010 from an
unknown source (and since edited occasionally to add known good default
passwords). Pulling those changes into this list probably would be
helpful to guess better.

As far as I can tell, there are no special licensing terms for these
lists.
Underscores because the rest are.
Land #1927 - Add common passwords from xato.net