add :nodoc: to AM::AttributeMethods#instance_method_already_implemented?...

Make the Resolver template cache threadsafe

add :nodoc: to AM::AttributeMethods::AttributeMethodMatcher

changed the firm of changes_from_zero_to_string?

Inflector: Added missing tests cases to ensure idempotency of singularize and pluralize

Removed warnings.

1. Change in test name as already defined.
2. ambiguous first argument; put parentheses or 
even spaces

This is a follow up to #4719. It appears that singularize and pluralize
are supposed to be idempotent - i.e. when you call singularize or
pluralize multiple times on the same string, you should get the same
result. (At least for the "officially supported" cases that the stock
inflector is designed to handle.) #4719 added the missing tests for
regular cases, and this commit added the missing tests for the
irregularities.

While I'm at that, I also synced up the irregularity test cases with
the current set of irregularity cases that we ship out-of-the-box.

delete *column* because is unused by the method.

Log listener is a singleton shared across threads, so make sure the
event queues are local to each thread.

Mailer with no implicit template

Refactor testcase codes. It's repeated.

Refactor db:structure:load task.

Fix GH #4259. When we execute schema dumper, we must remove table_name_prefix and table_name_suffix.

Add prev_quarter and next_quarter methods in Time/Date/DateTime calculations.

Similar to prev_month and next_month, it returns the date with the same day
in the previous or next quarter:

    t = Time.local(2010, 5, 8) # => Sat, 08 May 2010
    t.prev_quarter             # => Mon, 08 Feb 2010
    t.next_quarter             # => Sun, 08 Aug 2010

Closes #6402

Prevent concurrent compilation of templates - closes #6400

Correct the AP test。

Closes #6007

Also use if/else block to not use short circuit return

add :nodoc: to AV StylesheetIncludeTag, JavascriptIncludeTag and 
AssetIncludeTag [ci skip]

Fix #5990