Adds a merge config for Rails schema conflicts.

Rails schema version specification conflicts will always be resolved
using the newer schema version, picking the higher number.
Since it is unlikey any non-Rails projects will have a schema.rb
file where this rule would cause a problem it has been added globally
to .gitattributes rather than local to each individual Rails project.

Solution thanks to
http://tbaggery.com/2010/10/24/reduce-your-rails-schema-conflicts.html
Merge branch 'master' of github.com:mphstudios/dotfiles