Fix uniqueness validator for non-paranoid associations

real_destroy callback

Fix for #122, #121 and #175 on Rails 4 branch

Ruby 1.9's version of `Object.const_get` does not support namespaced constants, so this commit replaces it with `ActiveSupport`'s `#constantize` method.

The tests were failing running JRuby on 1.9 mode. CRuby was not failing because it is not tested against 1.9.

Fixes #114

Fix association class name for namespaced has one model lookups

Use association.klass.name instead of association.class_name to get the
namespaced class name and therefore prevent:

`Object.get_const(association_class_name)`

from raising "uninitialized constant ParanoidHasOne"
in the following situation:

module Something
  def self.table_name_prefix
    "something_"
  end

  class ParanoidHasOne < ActiveRecord::Base
    acts_as_paranoid
    has_one :paranoid_belongs_to, dependent: :destroy
  end

  class ParanoidBelongsTo < ActiveRecord::Base
    acts_as_paranoid
    belongs_to :paranoid_has_one
  end
end

hasOne = Namespaced::ParanoidHasOne.create
hasOne.destroy
hasOne.restore(:recursive => true) # previously would explode

add GoRails video to readme documentation

Fix typo

partial indexes advice

Update README.md

Remove table_name from where methods

Show the 'restore' instance method also in the code snippets

- `client.restore`
- `client.restore(:recursive => true)`

Fix counter cache behaviour on rails 4.2

This has been removed and should no longer exist.
https://github.com/radar/paranoia/pull/192#discussion_r24884921

I asked about `restore` in the
[Notes](https://github.com/radar/paranoia/pull/192#issue-51914917) of
the PR's description. Personally I don't need such a behaviour. So
removing.

remove unused parameter

This will allow to detect counter cached columns changes in callbacks
like `after_destroy` or `after_commit on: :destroy`.

My goal is Rails 4.2 support and it works well with Rails 4.2. I’m
leaving this bug not fixed for Rails 4.1 for the time being.

This is a workaround actually. Since
`ActiveRecord::CounterCache.each_counter_cached_associations` is
private. We shouldn’t use it. Proposals for the proper fix are welcome.

The reason the previous version stopped working is `affected_rows`
returns `0` at
[active_record/counter_cache.rb#L142](https://github.com/rails/rails/blo
b/ef99d4cd3ecc58a8c1484740b2fb5447dbda23ab/activerecord/lib/active_recor
d/counter_cache.rb#L142). If you follow the method call you’ll find
that it’s called at
[active_record/persistence.rb#L486](https://github.com/rails/rails/blob/
ef99d4cd3ecc58a8c1484740b2fb5447dbda23ab/activerecord/lib/active_record/
persistence.rb#L486). Probably we’d better override the return value in
`ActiveRecord::Relation.delete_all` at
[active_record/relation.rb#L481](https://github.com/rails/rails/blob/ef9
9d4cd3ecc58a8c1484740b2fb5447dbda23ab/activerecord/lib/active_record/rel
ation.rb#L481).

https://github.com/radar/paranoia/blame/1b051ae78793f3b62297b5adbaa9c1d0
0e6726e0/README.md#L154