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)
Speedup AS::Inflector.camelize

Benchmark:
          user     system      total        real
old   5.960000   0.020000   5.980000 (  5.981754)
new   5.740000   0.030000   5.770000 (  5.757201)
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
Speed up AS::Inflector.underscore

Benchmark:
          user     system      total        real
old   6.090000   0.120000   6.210000 (  6.202039)
new   5.930000   0.110000   6.040000 (  6.042022)
Merge pull request #10642 from LTe/invalid-load-error

Show real LoadError on helpers require
Speed up String#truncate

Benchmark:
          user     system      total        real
old   1.550000   0.040000   1.590000 (  1.585866)
new   1.250000   0.040000   1.290000 (  1.287693)
Speed up Array#split

Benchmark:
          user     system      total        real
old   0.510000   0.000000   0.510000 (  0.506749)
new   0.330000   0.000000   0.330000 (  0.336187)
Simplify Array#in_groups_of code
Remove accidentally committed vi .swp file.
Merge pull request #11391 from schuetzm/remove-swp-file

Remove accidentally committed vi .swp file.
Better not mutate the given options Hash
Add failing test for #9562

Rails 4.0.0 fails when trying to encode an ActiveSupport::TimeWithZone
that wraps a DateTime instance. This is fixed on master so add a test
to prevent regression.

(cherry picked from commit ad01b8da354268cebfae1519c28d19d75576ccb1)
Add missing require so that DateTime has the right superclass

If the DateTime core extensions were loaded before the Date core extensions
then you would get a superclass mismatch as DateTime hasn't been defined
yet so it gets set to Object by the acts_like core extension.

Fixes #11206
Add documentation for add_flash_types [ci skip]

Document a little bit the ActionController::Flash::add_flash_types
class method.
Merge pull request #11394 from robin850/patch-8

Add documentation for add_flash_types [ci skip]
 #11381: Ignore config.eager_load=true for rake

Closes #11381
Merge pull request #11389 from jetthoughts/11381_fix_hit_database_on_precompile

 #11381: Ignore config.eager_load=true for rake
Only raise DelegationError if it's is the source of the exception

This fixes situations where nested NoMethodError exceptions are masked
by delegations. This would cause confusion especially where there was a
problem in the Rails booting process because of a delegation in the
routes reloading code.

Fixes #10559
Add missing require
Fix a grammatical error/typo in Active Record Associations guide.