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

* remote:
  move fanout back to a global variable, add a mutex for safety

Refactor db:structure:dump task.

Remove extra test case.

Make the test description better reflect what is happening

Rename testcase name. It's wrong in the context.

Rename MySQLTestPurge to MySQLPurgeTest for consistency.

Refactor db:charset task

In a similar vein to Pat's work on create, drop etc, the db:charset
task is now a one liner in databases.rake