* Double-checked locking bug is fixed.
* @Nullable is removed since there is no need to use along with @MonotonicNonNull.
* Static import is removed.
* Lazy initialization is implemented.
* Local variables used instead of volatile ones.
* Local variables used instead of volatile ones.
`sessionToken`, `accessKey` and `secretKey` must be updated atomically.
Another race is possible between the file updater and the Druid process reading the file. It could be enforced only with mandatory file locking, but file locking is advisory by default in Linux.
* Add checkstyle rules about imports and empty lines between members
* Add suppressions
* Update Eclipse import order
* Add empty line
* Fix StatsDEmitter
* Rename io.druid to org.apache.druid.
* Fix META-INF files and remove some benchmark results.
* MonitorsConfig update for metrics package migration.
* Reorder some dimensions in inner queries for some reason.
* Fix protobuf tests.
* Use the official aws-sdk instead of jet3t
* fix compile and serde tests
* address comments and fix test
* add http version string
* remove redundant dependencies, fix potential NPE, and fix test
* resolve TODOs
* fix build
* downgrade jackson version to 2.6.7
* fix test
* resolve the last TODO
* support proxy and endpoint configurations
* fix build
* remove debugging log
* downgrade hadoop version to 2.8.3
* fix tests
* remove unused log
* fix it test
* revert KerberosAuthenticator change
* change hadoop-aws scope to provided in hdfs-storage
* address comments
* address comments
