No need to decorate columns twice

[ci skip] Fix doc for javascript_helper

We never want result types to override column types, and
`decorate_columns` can only affect column types. No need to go through
the decoration multiple times, we can just exclude the column types from
the result types instead.

Correct Bundler link [ci skip]

[ci skip] Refine Action Mailer guide.

* Wrap 80 words if possible.
* Make attachment hash options more readable. (L239-L243)

  Before:

  ![screenshot 2014-06-11 02 59 54](https://cloud.githubusercontent.com/assets/1000669/3235432/a91d0464-f0d2-11e3-9e4a-6af2b2a83f1a.png)

   After:

  ![screenshot 2014-06-11 02 59 36](https://cloud.githubusercontent.com/assets/1000669/3235428/a47b28dc-f0d2-11e3-806c-cfaedd3f15df.png)

* L619 Wrap "location" in code: `"location"`.
* L628 Use actual section name.
* L697 Remove unnecessary `./` when refer to other guide.

remove deprecation call while initializing `ClassCache` object

fix error with long keys in ActiveSupport::Cache::FileStore

[ci skip] Improve enable_starttls_auto documentation (Action Mailer).

[ci skip] Add Docs for strip_insignificant_zeros option in number_to_human

Remove deprecated method ActiveRecord::Base.quoted_locking_column

[ci skip] Correct output and use valid options of number helpers

Fix warnings in tests

```
activerecord/test/cases/adapters/postgresql/range_test.rb:159: warning: (...) interpreted as grouped expression
activerecord/test/cases/finder_test.rb:38: warning: shadowing outer local variable - e
activerecord/test/cases/finder_test.rb:43: warning: shadowing outer local variable - e
```

Keep the types of virtual columns after yaml serialization

remove depricated Validatior#setup

On MySQL and PostgreSQL, the adapter does not type cast virtual columns
for us.

Fix cache_digest rake tasks

Inline PG array type casting helper

Bring cache_digests:* rake tasks up-to-date with the API changes introduced in
637bb726

This is a follow up to #15602 which rendered the guides in a weird state:

  >  You can also specify some options just after the field type between curly
     braces. You can use the following modifiers:

  >  `null`         Allows or disallows `NULL` values in the column.

  >  NOTE: `null` and `default` cannot be specified via command line.

The modifiers are now moved into a separate section. The generator
simply referes to that section.

Related to #15583.

/cc @JuanitoFatas

[ci skip] Rename: Rails Database Migration to Active Record Migration.

This will need to setup permanent redirect for the old guide.

ActiveRecord::FinderMethods.find doesn't pass proc parameter to array

Manual merge of #15584.

Closes #15584.

[ci skip] Add note about type modifiers that cannot be specified in command line.