The main reason for this is that I want to separate the code that does
the mutating from the code that does the cloning.

(and changed the use of true for a more database agnostic example).

"Predicates in Rails rely on standard Ruby semantics for boolean values
and guarantee no singletons whatsoever." - @fxn

add test to show offset query_methods on mysql & mysql2

change test to cover public API

* Avoid double hash lookups in AR::Reflection when reflecting associations/aggregations
* Minor cleanups: use elsif, do..end, if..else instead of unless..else
* Simplify DynamicMatchers#respond_to?
* Use "where" instead of scoped with conditions hash
* Extract `scoped_by` method pattern regexp to constant
* Extract noisy class_eval from method_missing in dynamic matchers
* Extract readonly check, avoid calling column#to_s twice in persistence
* Refactor predicate builder, remove some variables

This reverts commit 5cad7a0d, reversing
changes made to bb842e8d.

And added NullRelation class implementing the null object pattern for the `Relation` class.

Character classes are the specific regexp construct
to express alternation of individual characters.

Also, fixed the bit about returning AM::MissingAttributeError. This
seems to be fixed earlier in 3-2-stable only.

See the CHANGELOG for details.

Fixes #950.