Drop graft alias and join_type arguments

JoinDependency#graft was dopped in activerecord and so was passing
join_type when constructing the nodes. See

https://github.com/rails/rails/commit/fadb6d923beb5a45650e6bb73c238538917c25e4
https://github.com/rails/rails/commit/ff5f328bdfdd3dffd31bd74adac9d1e6e7f241fd

This should at least let us load the code without things blow on start
up
Update specs and method signature in JoinAssociation
Remove a couple more deprecated JoinDependency api

Looking into the history for ActiveRecord::Associations::JoinDependency
should give us some help on why each one of those were removed. See for
example:

https://github.com/rails/rails/commit/868457488d3c43ff4e9c28e34883620d90345185
JoinDependency#build_with_polymorphism possibly works again

Looking at both +initialize+ and +build+ methods diff between Rails
4.0.2 and 4.1.0.beta1 should give some reasoning to the changes here.

It looks like all logic previously placed in JoinDependecy#build was
moved into some sort of tree so that all JoinDependecy#build does now is
find the reflection and build the JoinAssociation for that. Bad side
effect here is that JoinDependency#build_with_polymorphism overrides
rails ActiveRecord::JoinDependency#build completely.

https://github.com/rails/rails/blob/v4.0.2/activerecord/lib/active_record/associations/join_dependency.rb#L31-40
https://github.com/rails/rails/blob/v4.0.2/activerecord/lib/active_record/associations/join_dependency.rb#L128-154

https://github.com/rails/rails/blob/v4.1.0.beta1/activerecord/lib/active_record/associations/join_dependency.rb#L95-101
https://github.com/rails/rails/blob/v4.1.0.beta1/activerecord/lib/active_record/associations/join_dependency.rb#L214-225
Drop join_type examples in join_dependecy_spec

The accessor has been deprecated in rails core
JoinAssociation#build_constraint takes klass as first argument

See https://github.com/rails/rails/commit/743b67508e2027e1d086142ccbec47a19fc943f6
Add ActiveRecord namespace in EagerLoadPolymorphicError
Gemfile: use https for rubygems and Ruby 1.9+ hash syntax