Fixed an issue with service-specific configuration options.

Resolved an issue where service-specific configuration options
where not getting defined until the service class was autoloaded.
For example:

    require 'aws-sdk'
    AWS.config(:dynamo_db_crc_32_check => false) # oops, wont apply

    AWS::DynamoDB # autoload dynamo db service interface

    AWS.config(:dynamo_db_crc_32_check => false) # now it works

All service configurations are loaded up front now.

References #243