Expose method and class - so that we can use it from user code (particularly since checkpoint directory is autogenerated now
Address review comments
Use method, not variable
Address review comment
Correct L2 regularized weight update with canonical form
Merge pull request #437 from mridulm/master

Minor api usability changes

- Expose checkpoint directory - since it is autogenerated now
- null check for jars
- Expose SparkHadoopUtil : so that configuration creation is abstracted even from user code to avoid duplication of functionality already in spark.
Merge pull request #459 from srowen/UpdaterL2Regularization

Correct L2 regularized weight update with canonical form

Per thread on the user@ mailing list, and comments from Ameet, I believe the weight update for L2 regularization needs to be corrected. See http://mail-archives.apache.org/mod_mbox/spark-user/201401.mbox/%3CCAH3_EVMetuQuhj3__NdUniDLc4P-FMmmrmxw9TS14or8nT4BNQ%40mail.gmail.com%3E