Modified BlockManagerId API to ensure zero duplicate objects. Fixed BlockManagerId testcase in BlockManagerTestSuite.
Modified StorageLevel API to ensure zero duplicate objects.
Made StorageLevel constructor private, and added StorageLevels.create() to the Java API. Updates scala and java programming guides.
One more fix. Made even default constructor of BlockManagerId private to prevent such problems in the future.
Merge pull request #406 from tdas/master

Changed StorageLevel and BlockManagerId API to prevent duplication in memory