This reverts commit 408227d9, reversing
changes made to dca0b57d.

Fixes #9275.

When `#order` is called with a Symbol this patch will prepend the quoted_table_name.
Before the postgresql adapter failed to build queries containg a join and an order
with a symbol.

This expansion happens for all adapters.

Taking the wise advice of @carlosantoniodasilva

We discussed that the auto explain feature is rarely used.
This PR removes only the automatic explain. You can still display
the explain output for any given relation using `ActiveRecord::Relation#explain`.

As a side-effect this should also fix the connection problem during
asset compilation (#9385). The auto explain initializer in the `ActiveRecord::Railtie`
forced a connection.

The function is now called has_arguments? so that it's easier to tell
that it's just checking to see if the args are blank or not.

for query methods in a where_clause. Also, modified the CHANGELOG entry
because it had false information and added tests.

This caused a bug with the new associations implementation, because now
association conditions are represented as Arel nodes internally right up
to when the whole thing gets turned to SQL.

In Rails 3.2, association conditions get turned to raw SQL early on,
which prevents Relation#merge from interfering.

The current implementation was buggy when a default_scope existed on the
target model, since we would basically end up doing:

  default_scope.merge(association_scope)

If default_scope contained a where(foo: 'a') and association_scope
contained a where(foo: 'b').where(foo: 'c') then the merger would see
that the same column is representated on both sides of the merge and
collapse the wheres to all but the last: where(foo: 'c')

Now, the RHS of the merge is left alone.

Fixes #8990

closes #6865

This reverts commit 637a7d9d, reversing
changes made to 5937bd02.

There's no need to create a new arel table or reflect on the column
association if the value is empty, these attributes are not used.

Also no need to concat a new array, just append the query value.

* dependencies/autoload
* concern
* deprecation

Summary of the changes:
 * Add thread_safe gem.
 * Use thread safe cache for digestor caching.
 * Replace manual synchronization with ThreadSafe::Cache in Relation::Delegation.
 * Replace @attribute_method_matchers_cache Hash with ThreadSafe::Cache.
 * Use TS::Cache to avoid the synchronisation overhead on listener retrieval.
 * Replace synchronisation with TS::Cache usage.
 * Use a preallocated array for performance/memory reasons.
 * Update the controllers cache to the new AS::Dependencies::ClassCache API.
   The original @controllers cache no longer makes much sense after @tenderlove's
   changes in 7b6bfe84 and f345e238.
 * Use TS::Cache in the connection pool to avoid locking overhead.
 * Use TS::Cache in ConnectionHandler.

* Fix example queries
* Remove doc entries of where.like/not_like.
* Remove :chain from where.not related docs. To me that's an implementation
  detail and we don't expect people to use where(:chain).not.

The real win with these chain methods is where.not, that takes care of
different scenarios in a graceful way, for instance when the given value
is nil.

    where("author.id != ?", author_to_ignore.id)
    where.not("author.id", author_to_ignore.id)

Both where.like and where.not_like compared to the SQL versions doesn't
seem to give us that much:

    Post.where("title LIKE 'ruby on%'")
    Post.where.like(title: 'ruby on%'")
    Post.where("title NOT LIKE 'ruby on%'")
    Post.where.not_like(title: 'ruby on%'")

Thus Rails is adding where.not, but not where.like/not_like and others.

This commit stems from https://github.com/rails/rails/pull/8332#issuecomment-11127957

Since the formats in which conditions can be passed to `not` differ
from the formats in which conditions can be passed to `like` and `not_like`,
then I think it's worth adding rdoc and tests to show this behavior

Arel::Nodes::In inherits from Arel::Nodes::Equality, so the case
statement was always using the Equality operator for both scenarios,
resulting in a not equal query instead.

This commit updates the rdoc of AR#where to match the changes applied
in https://github.com/rails/rails/commit/6ba0f97 that is:

* `where(nil)` has the same effect of `where('')`: a no op
* `where` (no args) has the same effect of `where(:chain)`: to create a WhereChain