Remove unneeded require of rspec/core/project_initializer.

Each require takes time and it is a waste to require a file like this
that is so rarely used up front. Things that are rarely used should
be required at the point they are used rather than upfront.

lib/rspec/core.rb

@@ -28,7 +28,6 @@
 
 require_rspec['core/world']
 require_rspec['core/configuration']
-require_rspec['core/project_initializer']
 require_rspec['core/option_parser']
 require_rspec['core/configuration_options']
 require_rspec['core/command_line']

lib/rspec/core/option_parser.rb

@@ -96,6 +96,7 @@ def parser(options)
         end
 
         parser.on('--init', 'Initialize your project with RSpec.') do |cmd|
+          require 'rspec/core/project_initializer'
           ProjectInitializer.new(cmd).run
           exit
         end

spec/rspec/core/project_initializer_spec.rb

@@ -1,4 +1,5 @@
 require "spec_helper"
+require 'rspec/core/project_initializer'
 
 module RSpec::Core
   describe ProjectInitializer, :isolated_directory => true do