Respect NewCop value from merged_config

[ThomasKoppensteiner]

Rubocop 1.4.2 shows a warning about pending cops, even if the NewCops: enabled is set in a required config file.
This happens because the possible_new_cops? methods in the ConfigLoader checks against config and not against merged_config.

Warning Text:

The following cops were added to RuboCop, but are not configured. Please set Enabled to either `true` or `false` in your `.rubocop.yml` file.

Please also note that can also opt-in to new cops by default by adding this to your config:
  AllCops:
    NewCops: enable

---

Expected behavior

I expect that for the pending new cops check the merged configuration is considered and no warning is show when the NewCops setting is configured in a shared config file.

Actual behavior

The NewCops setting is not considered and the warning about pending new cops is shown.

Steps to reproduce the problem

Use 2 configuration files.

# File: .rubocop.yml
require:
- base

# NewCops is not set here
#
#  AllCops:
#    NewCops: enable

Base

# File: base.yml
AllCops:
  NewCops: enable

RuboCop version

Include the output of rubocop -V or bundle exec rubocop -V if using Bundler. Here's an example:

$ [bundle exec] rubocop -V
1.4.2 (using Parser 2.7.2.0, rubocop-ast 1.2.0, running on jruby 2.5.7 java)
  - rubocop-rspec 2.0.0

Solution

A possible solution is, as described above in the intro, to use merged_config instead of config for the check in the ConfigLoader.