pass arel to select_all rather than depend on method_missing
fix visibility of the relation construction methods
Remove unnecessary string interpolation

Removed from controller template of scaffold generator.
Merge pull request #11385 from MarceloCajueiro/remove_string_interpolation

Remove unnecessary string interpolation
Avoid creating an extra Range instance
Speedup String#to

Benchmark:
1000000.times { str.to(30) }
          user     system      total        real
old   0.490000   0.110000   0.600000 (  0.607374)
new   0.390000   0.000000   0.390000 (  0.387306)
Speedup AS::Inflector.deconstantize

Benchmark:
          user     system      total        real
old   0.740000   0.000000   0.740000 (  0.744358)
new   0.550000   0.000000   0.550000 (  0.553690)
Show real LoadError on helpers require

When helper try to require missing file rails will throw exception about
missing helper.

  # app/helpers/my_helper.rb

  require 'missing'

  module MyHelper
  end

And when we try do load helper

  class ApplicationController
    helper :my
  end

Rails will throw exception. This is wrong because there is a helper
file.

  Missing helper file helpers/my_helper.rb

Now when helper try to require non-existed file rails will throw proper
exception.

  No such file to load -- missing