Add more debug message for ManagedBuffer

[rxin]

This is to help debug the error reported at http://apache-spark-user-list.1001560.n3.nabble.com/SQL-queries-fail-in-1-2-0-SNAPSHOT-td15327.html

[SparkQA]

QA tests have started for PR 2580 at commit 323dfec.

• This patch merges cleanly.

[Ishiihara]

Two less spaces before '}'

[rxin]

No the indent was correct.

[Ishiihara]

Sorry I looked the wrong line.

[SparkQA]

QA tests have started for PR 2580 at commit 5814292.

• This patch merges cleanly.

[aarondav]

LGTM once Travis passes.

[SparkQA]

QA tests have finished for PR 2580 at commit 323dfec.

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

[AmplabJenkins]

Test PASSed.
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[aarondav]

Merging into master.

[SparkQA]

QA tests have finished for PR 2580 at commit 5814292.

• This patch passes unit 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/20985/