Moved "`mod_expires` to be enabled" to new line.

- Right now the comment was not rendering properly.
  # The Expires* directives requires the Apache module
  `mod_expires` to be
  # enabled.
- After this change -
  # The Expires* directives requires the Apache module
  # `mod_expires` to be enabled.
Removing merge conflict remnants in the guides.
Document ability to run a single test.
Fix doc for singularize - `pluralized` => `singularized`
Note functional equivalence in reset task
Add documentation for rake db:setup task
Fix typos [ci skip]
FIX reload! within rails console --sandbox causes undefined method rollback upon exiting [https://github.com/rails/rails/issues/11834]
add missing fixtures file
Merge pull request #12085 from valk/master

FIX reload! within rails console --sandbox causes undefined method rollb...
Merge branch 'master' of github.com:rails/docrails
cache misses should return self
Don't create fibers just to iterate
require a class for cache computations
no need for the const_get since we lock
add a failing test for marshal + cache problems
move the cache to the AR models and populate it on inherited
no need to fully qualify
remove unused variable
reduce relation allocations