Refactored pluralize and singularize into a common method

See diff discussion on rails/#3536.

Update ActiveRecord#attribute_present? to work as documented

"Returns true if the specified attribute has been set by the user or by
a database load and is neither nil nor empty?"

Fixes #1613

This is a first implementation, EXPLAIN is highly
dependent on the database and I have made some
compromises.

On one hand, the method allows you to run the most
common EXPLAIN and that's it. If you want EXPLAIN
ANALYZE in PostgreSQL you need to do it by hand.

On the other hand, I've tried to construct a string
as close as possible to the ones built by the
respective shells. The rationale is that IMO the
user should feel at home with the output and
recognize it at first sight. Per database.

I don't know whether this implementation is going
to work well. Let's see whether people like it.

Add arel to Gemfile on apps generated in edge Rails

Fixed an issue id false option is ignored on mysql/mysql2 (fix #3440)

This reverts commit 6aaae3de, reversing
changes made to fdbc4e5f.

Reason: build failure.

This test is affected by a bug in Ruby 1.9.3p0 and trunk:
http://redmine.ruby-lang.org/issues/5564

Given we cannot fix it for ourselves, it is better to skip for now so
that we will easily see if further failures are introduced.

Jon Leighton is monitoring the bug report and will revert this when a
suitable solution is found (either a new Ruby release or a generic
workaround).

If you are using 1.9.3 in your app and have templates that are not in
UTF-8, you should add a workaround early on in the boot process. For
example, if your templates are Shift_JIS encoded, then add the
following in an initializer:

Encoding::Converter.new('Shift_JIS', 'UTF-8')

Remove warnings by calling remove_method

This reverts commit d163d3bf.

Reason: The alternate approach can be documented in the guide and
not disrupt the existing flow in the readme.

This reverts commit 36a5f48f.

Reason: Editing .gitignore in docrails is not allowed. Docrails is meant
only for documentation.

AR changes to support creating ordered (asc, desc) indexes

Defining after_initialize and after_find as ordinary methods like documented
in the guide doesn't work with Rails 3.1.1; now macro-style is used here, too.

Fix test as one more has_many added

Synchronize the gemspecs since CHANGELOG has been renamed to CHANGELOG.md

Reasons:

 * Markdown reads well as plain text, but can also be formatted.
 * It will make it easier for people to read on the web as Github
   formats the Markdown nicely.
 * It will encourage a level of consistency when people are writing
   CHANGELOG entries.

The script used to perform the conversion is at
https://gist.github.com/1339263

This is to avoid confusing newbies, and to be consistent with the fact
that other options like :foreign_key already allow a symbol or a string.

Remove 'size' attribute from number_field form helper fixes #3454

Sexier migrations

f.number_field generates <input type="number", size="30"../> which is
invalid HTML5. See: http://dev.w3.org/html5/spec/Overview.html#number-state

Preserve SELECT columns on the COUNT for finder_sql when possible

This is in response to rails/rails#3504.

Stub find_template so that when handle_render_error is called in ActionView::Template, we get to see the actual underlying error rather than a NoMethodError.

This shows an encoding bug on Ruby 1.9.3.