Fix database tasks in test namespace.

This is mostly the same as 876bade5
that was reverted due to test failures, but now with a correction.

This reverts commit a0edfb4d, reversing
changes made to 4012fcff.

Fix database tasks in test namespace.

Make structure.sql file configureable in db:structure:dump analog to SCHEMA in db:schema:dump

bypass preloading for ids_reader

call scope within unscoped to prevent duplication of where values

Warning removed in test

when fetching ids for a collection, bypass preloading
to avoid the unnecessary performance overhead

No need 'abstract_unit' here. It's already in 'generators_test_helper'

Rake tasks generator

Add Help Text to Routing Error

When a newcomer hits the routing error page they
are often confused about how to trouble shoot the
next step. Adding a simple help text can gently 
remind coders where to get more help.

Allow symbols to be passed as extension aliases in Mime::Type.register

Fixed test "ArgumentError: wrong number of arguments(1 for 0)"

warning removed "warning: instance variable @variable_for_layout not ini...

Fix expanding cache key for single element arrays

Fixed bug when error message is an empty string.

Fix favicon_link_tag help text