Remove hard dependency on bcrypt.

Gemfile

@@ -6,6 +6,7 @@ if ENV['AREL']
   gem "arel", :path => ENV['AREL']
 end
 
+gem "bcrypt-ruby", "~> 3.0.0"
 gem "jquery-rails"
 # This needs to be with require false to avoid
 # it being automatically loaded by sprockets

activemodel/activemodel.gemspec

@@ -19,5 +19,4 @@ Gem::Specification.new do |s|
   s.add_dependency('activesupport', version)
   s.add_dependency('builder',       '~> 3.0.0')
   s.add_dependency('i18n',          '~> 0.6')
-  s.add_dependency('bcrypt-ruby',   '~> 3.0.0')
 end

activemodel/lib/active_model/secure_password.rb

@@ -1,5 +1,3 @@
-require 'bcrypt'
-
 module ActiveModel
   module SecurePassword
     extend ActiveSupport::Concern
@@ -30,6 +28,9 @@ module ActiveModel
       #   User.find_by_name("david").try(:authenticate, "notright")      # => nil
       #   User.find_by_name("david").try(:authenticate, "mUc3m00RsqyRe") # => user
       def has_secure_password
+        gem 'bcrypt-ruby', '~> 3.0.0'
+        require 'bcrypt'
+
         attr_reader :password
 
         validates_confirmation_of :password