such as, cough cough, the SQL execution ID. This was a problem
because scala's parallel collections spawns threads as children
of the existing threads, causing the execution ID to be inherited
when it shouldn't be.

Because java.util.Properties' remove method takes in an Any
instead of a String, there were some issues with matching the
key's hashCode, so removing was not successful in unit tests.

Instead, this commit fixes it by manually filtering out the keys
and adding them to the child thread's properties.

…executions

... to make the behavior more consistent in SQL vs non-SQL cases.

…executions

Conflicts:
	core/src/test/scala/org/apache/spark/ThreadingSuite.scala

…executions

The fix for SPARK-10548 can be simplified by just cloning the
parent properties on inherit rather than excluding specific
properties from ever being inherited. This is safe because the
child thread must be created BEFORE the parent thread runs a
query.

…executions

…executions

Conflicts:
	core/src/test/scala/org/apache/spark/ThreadingSuite.scala