add services: memcache to travis

The :source option for has_many => through should accept String values.

values.

With the changes introduced by 16b70fdd
it was expecting the value to be a Symbol, while it could be also a
String value.

Avoid URI parsing

This parsing is unecessary once the Request object already has the
needed information.

Add missing require so requiring `active_support/cache` works again.

Expand explanation of how to set secrets.yml.

Guides: minor typo fixed in Asset Pipeline guide

Fixed problem where `1.day.eql?(1.day)` is false

This fixes:
    1.second.eql?(1.second) #=> false

The new `eql?` requires that `other` is an `ActiveSupport::Duration`.
This requirement makes `ActiveSupport::Duration`'s behavior consistent
with other numeric types in Ruby.

    1.eql?(1.0) #=> false
    1.0.eql?(1) #=> false

    1.second.eql?(1) #=> false (was true)
    1.eql?(1.second) #=> false

    { 1 => "foo", 1.0 => "bar" }
    #=> { 1 => "foo", 1.0 => "bar" }

    { 1 => "foo", 1.second => "bar" }
    # now => { 1 => "foo", 1.second => "bar" }
    # was => { 1 => "bar" }

And though the behavior here hasn't changed, for reference:

    1 == 1.0 #=> true
    1.0 == 1 #=> true

    1 == 1.second #=> true
    1.second == 1 #=> true

Updates the maintenance policy with new Rails versions

Only apply DATABASE_URL for Rails.env

In passing, allow multi-word adapters to be referenced in a URL:
underscored_name must become hyphened-name.

The "DATABASE_URL_*" idea was moving in the wrong direction.

Instead, let's deprecate the situation where we end up using
ENV['DATABASE_URL'] at all: the Right Way is to explicitly include it in
database.yml with ERB.

.. even when the supplied config made no hint that name was relevant.

If the supplied string doesn't contain a colon, it clearly cannot be a
database URL. They must have intended to do a key lookup, so even though
it failed, give the explanatory deprecation warning, and raise the
exception that lists the known configs.

Conveniently, this also simplifies our logical behaviour: if the string
matches a known configuration, or doesn't contain a colon (and is
therefore clearly not a URL), then we output a deprecation warning, and
behave exactly as we would if it were a symbol.

This seems to simplify the operative part. Most importantly, by
pre-loading all the configs supplied in ENV, we ensure the list is
complete: if the developer specifies an unknown config, the exception
includes a list of valid ones.

configuration

As we like ENV vars, also support DATABASE_URL_#{env}, for more obscure
use cases.

The original attempt didn't really fix the problem and wasn't testing the
problematic area. This commit corrected those issues in the original commit.

Also removed the private `enum_mapping_for` method. As `defined_enums` is now a
method, this method doesn't provide much value anymore.

Build the reverse_order on its proper method.

remove check for present? from delete_all method