Celluloid 0.16.0.pre3 issue description: When running these quite small actors in a supervised pool, they do not start they are not available in the Celluloid::Actor[] registry as they were in v0.15.2.

Gemfile

#gem	'celluloid', '>= 0.16.0.pre3'
gem	'celluloid', '>= 0.15.2'
gem 'rspec'

Gemfile.lock

GEM
  specs:
    celluloid (0.15.2)
      timers (~> 1.1.0)
    diff-lcs (1.2.5)
    rspec (3.0.0)
      rspec-core (~> 3.0.0)
      rspec-expectations (~> 3.0.0)
      rspec-mocks (~> 3.0.0)
    rspec-core (3.0.4)
      rspec-support (~> 3.0.0)
    rspec-expectations (3.0.4)
      diff-lcs (>= 1.2.0, < 2.0)
      rspec-support (~> 3.0.0)
    rspec-mocks (3.0.4)
      rspec-support (~> 3.0.0)
    rspec-support (3.0.4)
    timers (1.1.0)

PLATFORMS
  ruby

DEPENDENCIES
  celluloid (>= 0.15.2)
  rspec

lib-small_actor.rb

require 'celluloid'

class SmallActor
  include Celluloid

  def example_method
    :dude
  end
end

class SmallActorSupervisor < Celluloid::SupervisionGroup
  pool SmallActor, as: :small_actor
end
SmallActorSupervisor.run!  

class SmallInterface
  def method_missing(method_sym, *arguments, &block)
    Celluloid::Actor[:small_actor].public_send(method_sym, *arguments, &block)
  end
end

spec-small_actor_spec.rb

require "small_actor"

describe SmallActor do
  before do
  	Celluloid.boot
  	sleep 0.1
  	Celluloid::Actor[:small_actor].example_method
  end

  after	do
  	Celluloid.shutdown
  end

  it 'is running' do
  	expect(Celluloid::Actor[:small_actor]).not_to be_nil
  end

end