Only cache template digests if config.cache_template_loading

since ActionView::Resolver.caching is set to the same value as config.cache_template_loading
only cache template digests if config.cache_template_loading is not falsy
fixes issues #10752 and #10791
Remove extra case.
Add error message for including nokogiri in Gemfile for rake doc:guides [ci skip]

- When `rake doc:guides` is run from applications, it complains for
  presence of redcarpet if it not present in Gemfile
- Similarly it should complain about nokogiri
Display exceptions in text format for xhr request
Making proper_table_name take in options.

The options will specify the prefix and the suffix. Also, I'm moving the
method to be an instance method on the +Migration+ instance. This makes more
sense than being a class method on the +Migrator+ class because the only
place that uses it is on a +Migration+ instance (in a method_missing
hook). The logic for the Migrator shouldn't be doing any work to
calculate the table name, it should be the Migration itself.

Also made some small indentation fixes.
Add a note about edge guides in the feedback section[ci skip]
Merge pull request #11991 from prathamesh-sonpatki/note-edge-guides

Add a note about edge guides in the feedback section [ci skip]
remove unused instance variable
Merge pull request #11994 from rajcybage/fix_instance

remove not used instance variable
Fix typo in file path, should include extension.
Adds Akshay Surve to Rails Guides credits list

I had written the original guide for "A Guide to Testing Rails
Applications". The current documents maintains the same structure and
examples I had drafted albeit with some minor changes to keep up with
newer version of Rails.

Older version which had credits included:
http://guides.rubyonrails.org/v2.3.11/testing.html

Github lifo/docrails History:
https://github.com/rails/rails/commits/ff359af86505b4d317b7467e7f79aa2ef2c5e795/railties/doc/guides/source/testing_rails_applications.txt
Merge pull request #11996 from semaperepelitsa/master

Docs: fix typo in file path, should include extension. [ci skip]
cleans the guides sources from fancy non-ASCII stuff
Deprecating passing strings as class name in fixtures.
Merge pull request #11960 from kirs/xhr-errors

Show exceptions in text format for xhr requests
typo [ci skip]
Merge pull request #11984 from wangjohn/proper_table_name

Making proper_table_name take in options.
Merge pull request #12000 from wangjohn/deprecating_class_name_string_in_fixtures

Deprecating passing strings as class name in fixtures.
Adding deprecation assertions for proper_table_name.

This prevents deprecation warnings from popping up.
Merge pull request #12008 from wangjohn/skipping_deprecated_migration_tests

Skip tests using deprecated +proper_table_name+ method.