Merge pull request #298 from nextgearcapital/master

Rails 4 Support
moved arel classes/modules to separate files, no functional difference
no longer necessary to specify encoding
arel now supports comparisons, but we still need to override the eql? method for Ordering
pass a to all visitor calls
Fix warning about already defined EXPLAINED_SQLS
Merge pull request #300 from wok/master

Fix warning about already defined EXPLAINED_SQLS
Merge branch 'master' of https://github.com/rails-sqlserver/activerecord-sqlserver-adapter