[SPARK-2518][SQL] Fix foldability of Substring expression.

This is a follow-up of #1428.

Author: Takuya UESHIN <ueshin@happy-camper.st>

Closes #1432 from ueshin/issues/SPARK-2518 and squashes the following commits:

37d1ace [Takuya UESHIN] Fix foldability of Substring expression.
[SPARK-2517] Remove some compiler warnings.

Author: Reynold Xin <rxin@apache.org>

Closes #1433 from rxin/compile-warning and squashes the following commits:

8d0b890 [Reynold Xin] Remove some compiler warnings.
[SPARK-2522] set default broadcast factory to torrent

HttpBroadcastFactory is the current default broadcast factory. It sends the broadcast data to each worker one by one, which is slow when the cluster is big. TorrentBroadcastFactory scales much better than http. Maybe we should make torrent the default broadcast method.

Author: Xiangrui Meng <meng@databricks.com>

Closes #1437 from mengxr/bt-broadcast and squashes the following commits:

ed492fe [Xiangrui Meng] set default broadcast factory to torrent
fix compile error of streaming project

explicit return type for implicit function

Author: James Z.M. Gao <gaozhm@mediav.com>

Closes #153 from gzm55/work/streaming-compile and squashes the following commits:

11e9c8d [James Z.M. Gao] fix style error
fe88109 [James Z.M. Gao] fix compile error of streaming project
[SPARK-2317] Improve task logging.

We use TID to indicate task logging. However, TID itself does not capture stage or retries, making it harder to correlate with the application itself. This pull request changes all logging messages for tasks to include both the TID and the stage id, stage attempt, task id, and task attempt.  I've consulted various people but unfortunately this is a really hard task.

Driver log looks like:

```
14/06/28 18:53:29 INFO DAGScheduler: Submitting 10 missing tasks from Stage 0 (MappedRDD[1] at map at <console>:13)
14/06/28 18:53:29 INFO TaskSchedulerImpl: Adding task set 0.0 with 10 tasks
14/06/28 18:53:29 INFO TaskSetManager: Re-computing pending task lists.
14/07/15 19:44:40 INFO TaskSetManager: Starting task 0.0 in stage 1.0 (TID 0, localhost, PROCESS_LOCAL, 1855 bytes)
14/07/15 19:44:40 INFO TaskSetManager: Starting task 1.0 in stage 1.0 (TID 1, localhost, PROCESS_LOCAL, 1855 bytes)
14/07/15 19:44:40 INFO TaskSetManager: Starting task 2.0 in stage 1.0 (TID 2, localhost, PROCESS_LOCAL, 1855 bytes)
14/07/15 19:44:40 INFO TaskSetManager: Starting task 3.0 in stage 1.0 (TID 3, localhost, PROCESS_LOCAL, 1855 bytes)
14/07/15 19:44:40 INFO TaskSetManager: Starting task 4.0 in stage 1.0 (TID 4, localhost, PROCESS_LOCAL, 1855 bytes)
14/07/15 19:44:40 INFO TaskSetManager: Starting task 5.0 in stage 1.0 (TID 5, localhost, PROCESS_LOCAL, 1855 bytes)
14/07/15 19:44:40 INFO TaskSetManager: Starting task 6.0 in stage 1.0 (TID 6, localhost, PROCESS_LOCAL, 1855 bytes)
...
14/07/15 19:44:40 INFO TaskSetManager: Finished task 1.0 in stage 1.0 (TID 1) in 64 ms on localhost (4/10)
14/07/15 19:44:40 INFO TaskSetManager: Finished task 4.0 in stage 1.0 (TID 4) in 63 ms on localhost (5/10)
14/07/15 19:44:40 INFO TaskSetManager: Finished task 2.0 in stage 1.0 (TID 2) in 63 ms on localhost (6/10)
14/07/15 19:44:40 INFO TaskSetManager: Finished task 7.0 in stage 1.0 (TID 7) in 62 ms on localhost (7/10)
14/07/15 19:44:40 INFO TaskSetManager: Finished task 6.0 in stage 1.0 (TID 6) in 63 ms on localhost (8/10)
14/07/15 19:44:40 INFO TaskSetManager: Finished task 9.0 in stage 1.0 (TID 9) in 8 ms on localhost (9/10)
14/07/15 19:44:40 INFO TaskSetManager: Finished task 8.0 in stage 1.0 (TID 8) in 9 ms on localhost (10/10)

```

Executor log looks like
```
14/07/15 19:44:40 INFO Executor: Running task 0.0 in stage 1.0 (TID 0)
14/07/15 19:44:40 INFO Executor: Running task 3.0 in stage 1.0 (TID 3)
14/07/15 19:44:40 INFO Executor: Running task 1.0 in stage 1.0 (TID 1)
14/07/15 19:44:40 INFO Executor: Running task 4.0 in stage 1.0 (TID 4)
14/07/15 19:44:40 INFO Executor: Running task 2.0 in stage 1.0 (TID 2)
14/07/15 19:44:40 INFO Executor: Running task 5.0 in stage 1.0 (TID 5)
14/07/15 19:44:40 INFO Executor: Running task 6.0 in stage 1.0 (TID 6)
14/07/15 19:44:40 INFO Executor: Running task 7.0 in stage 1.0 (TID 7)
14/07/15 19:44:40 INFO Executor: Finished task 3.0 in stage 1.0 (TID 3). 847 bytes result sent to driver
14/07/15 19:44:40 INFO Executor: Finished task 2.0 in stage 1.0 (TID 2). 847 bytes result sent to driver
14/07/15 19:44:40 INFO Executor: Finished task 0.0 in stage 1.0 (TID 0). 847 bytes result sent to driver
14/07/15 19:44:40 INFO Executor: Finished task 1.0 in stage 1.0 (TID 1). 847 bytes result sent to driver
14/07/15 19:44:40 INFO Executor: Finished task 5.0 in stage 1.0 (TID 5). 847 bytes result sent to driver
14/07/15 19:44:40 INFO Executor: Finished task 4.0 in stage 1.0 (TID 4). 847 bytes result sent to driver
14/07/15 19:44:40 INFO Executor: Finished task 6.0 in stage 1.0 (TID 6). 847 bytes result sent to driver
14/07/15 19:44:40 INFO Executor: Finished task 7.0 in stage 1.0 (TID 7). 847 bytes result sent to driver
```

Author: Reynold Xin <rxin@apache.org>

Closes #1259 from rxin/betterTaskLogging and squashes the following commits:

c28ada1 [Reynold Xin] Fix unit test failure.
987d043 [Reynold Xin] Updated log messages.
c6cfd46 [Reynold Xin] Merge branch 'master' into betterTaskLogging
b7b1bcc [Reynold Xin] Fixed a typo.
f9aba3c [Reynold Xin] Made it compile.
f8a5c06 [Reynold Xin] Merge branch 'master' into betterTaskLogging
07264e6 [Reynold Xin] Defensive check against unknown TaskEndReason.
76bbd18 [Reynold Xin] FailureSuite not serializable reporting.
4659b20 [Reynold Xin] Remove unused variable.
53888e3 [Reynold Xin] [SPARK-2317] Improve task logging.