SPARK-6225 [CORE] [SQL] [STREAMING] Resolve most build warnings, 1.3.0 edition

[srowen]

Resolve javac, scalac warnings of various types -- deprecations, Scala lang, unchecked cast, etc.

[SparkQA]

Test build #28392 has started for PR 4950 at commit c67985b.

• This patch merges cleanly.

[srowen]

In case you're wondering: no this wasn't one of those things deprecated in Hadoop 2.x; this was deprecated in 1.0.4 even!

[SparkQA]

Test build #28392 has finished for PR 4950 at commit c67985b.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[AmplabJenkins]

Test PASSed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/28392/
Test PASSed.

[tdas]

LGTM for changes related to streaming files.

[jkbradley]

ditto (organize imports)

[jkbradley]

LGTM for MLlib. @srowen Thanks for taking the time to do these cleanups!

[rxin]

lgtm

[SparkQA]

Test build #28406 has started for PR 4950 at commit 3080972.

• This patch merges cleanly.

[SparkQA]

Test build #28406 has finished for PR 4950 at commit 3080972.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[AmplabJenkins]

Test PASSed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/SparkPullRequestBuilder/28406/
Test PASSed.