Fixed `columns_for_distinct` of postgresql adapter
Added partial days support to `DateTime`'s `advance` method.

You can now add partial days (e.g. 2.5.days) to `DateTime` with the advance method.
This was acheived by mimicing the `advance` implementation in `Time`.
Fixed changelog
Added documentation for the :param option for resourceful routing
skip migration check if adapter doesn't support it
Swallow bundler exceptions when running tests

Let's avoid useless output when testing stuff related to Bundler.
Remove unnecessary include for integration tests.
:scissors:
Fix Baseclass becomes! subclass.
WIP: pass existing joins to construct_join_dependency
Merge pull request #15210 from arthurnn/fix_hbtm_reflection

Fix habtm reflection
Conflicts:
    activerecord/CHANGELOG.md
    activerecord/lib/active_record/counter_cache.rb
    activerecord/lib/active_record/reflection.rb
    activerecord/test/cases/reflection_test.rb
Use .to_s on _reflections lookup
Skip if the association was already loaded.
Improve readability of Explain Queries table in guides [ci skip]
Merge pull request #15303 from JohnKellyFerguson/guides-ar-querying

Improve readability of Explain Queries table in guides
integration tests do not need to load fixtures by hand

I don't know when this changed, checked back up to 3.2 and integration
tests instantiate fixtures just fine.
Update all Rails 4.1.0 references in guides to 4.1.1 [ci skip]
Merge pull request #15304 from JohnKellyFerguson/guides-4.1.1

Update all Rails 4.1.0 references in guides to 4.1.1 [ci skip]
unwrap the constraints object on initialization, eliminate loops

Unwrap Constraints objects.  I don't actually think it's possible
to pass a Constraints object to this constructor, but there were
multiple places that kept testing children of this object.  I
*think* they were just being defensive, but I have no idea.
Always construct route objects with Constraint objects