Bump version to 0.4.0-alpha

Hello @nicks, 

Please review the following commits I made in branch 'xiao-bump-version'.

80cf4d1820d49137d93d60cff24fee12051ad0b6 (2014-04-02 14:53:15 -0700)
Bump version to 0.4.0-alpha

R=@nicks