Fix for compatibility issue with exim

Hi,
Where I work at the university of Luxembourg, they are using exim and I needed to change a few things in order to fix a compatibility issue explained here : https://github.com/gitlabhq/gitlabhq/issues/4866
And the current template "application.rb.erb" is not compatible with gitlab since the version 6.8 I think. So I updated it.
Thanks.