Stop testing on 1.8.7, 1.9.2, rbx-18mode, and rbx-19mode.
Adding Rails 4 and its dependent gems.

Unfortunately we can't just use only activerecord, since it's not released as stand alone gem.

Also:
* Replacing all .scoped calls with .all
* Using new order syntax on AR associations
* Replaced deprecated finder methods
* Using to_a for comparing activerecord relations in specs.
* Using correct activerecord syntax in nested_set_scope method
Use only activerecord, not all of Rails.
attr_accessible was removed from activerecord.
Let specs run and fix deprecation warnings about default_scope.
Delegate connection to class

Rails 4 has deprecated the instance connection method, this adds a delegation method back to skip the deprecation warning
move hardcode id to primary_key
Oracle does not support locks in subquery

Issue #166
using the quoted order column name
Merge pull request #188 from kangguru/master

Quote order_column_name
Merge pull request #186 from superimmo/master

Move hardcode id to primary_key
Merge pull request #187 from jhanggi/oracle_lock_166

Issue #166 Oracle does not support locks in subquery
Merge pull request #184 from lexrupy/rails4

Delegate connection to class
Fix ordering for left_sibling
Remove left_sibling order clause completely.

This is already handled by siblings via nested_set_scope
Refactor into existing or new methods where possible.
without_self returns scope when not persisted.

Fixes #157
pulled out the columns and model modules into their own files, and pulled out the move_to logic into its own object
pull out pruning logic into its own module and split up complex method
pull out moving logic into its own module and break up complex methods