Description:
    ruby script/generate add_authlogic_rpx_migration [mapping:mapping_mode] [user_model:model_name] 
    
    Creates an add_authlogic_rpx_migration file in db/migrate.
    
    The mapping_mode parameter indicates which style of Authlogic_RPX-supported identity 
    mapping should be used. Allowed values for mapping_mode are:
       none
       internal 
    Default mapping_mode is 'internal'
    
    The user_model parameter specifies the name of the user/member model in your application.
    Default model_name is 'User'

    e.g. to generate the RPX migration where the user model is called 'Member' and you do not
    want to support identity mapping:
    
    ruby script/generate add_authlogic_rpx_migration mapping:none user_model:member
