rb: Reorganize the Rakefile a bit [THRIFT-38]

From kevin@rapleaf.com

Also add a guard to ensure `rake test` is only run if we're in a full thrift checkout


git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@670981 13f79535-47bb-0310-9956-ffa450edef68
1 file changed