Zero has one digit, but Math.log10(0) returns -Infinity. The method
needs to special-case zero.

The patch adds a regression test that is not clearly related to the
underlying issue because digit_count is private and has no coverage.
Gray area.

This bug was uncovered by 60062cf3.

don't log errors when all is fine

Move as/test_test to as/test_case_test

Revert "Do not gsub non ASCII characters in header anchor.".

This reverts commit 699babe8.

Also change the upgrading_ruby_on_rails link back to original in 4_2_release_notes.

Updated the deprecation warnings to 5.0

Remove end-of-line spacing in development.rb, production.rb

Also moved comment for removal above `unless()` to not confuse RDoc with
the documentation for this method.

Remove global helpers from the ActionMailer test suite.

Add `set_delivery_method` and `restore_delivery_method` to `ActionMailer::TestCase.

This way these methods are available outside the ActionMailer test suite, but
they are still duplicated inside `test/abstract_unit` for test cases that don't
inherit from the `ActionMailer::TestCase` class.

A combination of two commits led into these failures:

* The addition of a new active_record config in
  24bb8347
* The revert of the config to use config.x as options holder in
  43073b39

These tests remove activerecord from the load path, however the
configuration is still in the application file, and they blow up.

CSRF token mask from breach-mitigation-rails gem

[Godfrey Chan, Genadi Samokovarov]

Previously setting simple values to the config.x object resulted in the
following:

    config.x.super_debugger = true
    config.x.super_debugger #=> {}

Which was against the examples showed in the changelog/release notes.

Godfrey Chan, Genadi Samokovarov