Fixed `columns_for_distinct` of postgresql adapter
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.
Remove duplicated HashWithIndifferentAccess#with_indifferent_access.
[ci skip] Fix Compiler's Github link
Speed-up TimeWithZone to String conversion

I've noticed that `String(model.created_at)` is performing poorly in comparision
with other fields. The source of the problem is a way `Kernel#String` works: it first
tries to call `to_str` (which causes `NoMethodError` in `method_missing`) and then calls `to_s`.

Performance tests:

    tz = Time.zone.now

    Benchmark.ips do |x|
      x.report { String(tz) }
    end

Without this code:

    Calculating -------------------------------------
                               572 i/100ms
    -------------------------------------------------
                            10177.7 (±18.2%) i/s -      48620 in   5.000325s

With this code:

    Calculating -------------------------------------
                              1518 i/100ms
    -------------------------------------------------
                           138984.2 (±10.1%) i/s -     677028 in   4.974897s
Move types to the top level `ActiveRecord` namespace

`ActiveRecord::ConnectionAdapters::Type::Value` =>
`ActiveRecord::Type::Value`
Initial doc for TransactionIsolationError [ci skip]
Add with_default_charset helper.
Merge pull request #15381 from zuhao/refactor_actionpack_content_type_test

Add with_default_charset helper.
Move I18n.locale setting into setup and teardown.
Merge pull request #15383 from zuhao/refactor_actionpack_localized_templates_test

Move I18n.locale setting into setup and teardown.
Add and remove renderer inside the test to prevent leak.
Avoid hardcoded value in teardown.
Merge pull request #15385 from zuhao/refactor_actionpack_render_other_test

Add and remove renderer inside the test to prevent leak.
Remove unused `Column#coder`

It appears this property was added, but never actually used. It would be
broken if it were, as it only type casts one way.