skip migration check if adapter doesn't support it
Added missing test case for migrations when using sql structure
Prevent state leak.
Remove redundant code.
Refactor determination of max updated timestamp

`[].max # => nil`
Silence 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
```
Merge pull request #15610 from sgrif/silence-warnings

Fix warnings in tests
[ci skip] Correct output and use valid options of number helpers
Remove deprecated method ActiveRecord::Base.quoted_locking_column
Merge pull request #15611 from akshay-vishnoi/doc_changes

[ci skip] Correct output and use valid options of number helpers
[ci skip] Add Docs for strip_insignificant_zeros option in number helpers
Merge pull request #15612 from akshay-vishnoi/delete-deprecated-method

Remove deprecated method ActiveRecord::Base.quoted_locking_column
[ci skip] Improve enable_starttls_auto documentation.
fix error with long keys in ActiveSupport::Cache::FileStore
Merge pull request #15614 from akshay-vishnoi/doc_changes

[ci skip] Add Docs for strip_insignificant_zeros option in number_to_human
Merge pull request #15615 from JuanitoFatas/doc/action-mailer

[ci skip] Improve enable_starttls_auto documentation (Action Mailer).
Merge pull request #15616 from apanzerj/fix_long_key_paths

fix error with long keys in ActiveSupport::Cache::FileStore
remove deprecation call while initializing `ClassCache` object
Merge pull request #15617 from kuldeepaggarwal/remove-deprecate-method

remove deprecation call while initializing `ClassCache` object
[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.