Use string comparison for TaskID.

Review: https://reviews.apache.org/r/11488
s/hadoopJobs/jobs/g in Hadoop scheduler.

Review: https://reviews.apache.org/r/11489
Refactor Hadoop job completion.

Review: https://reviews.apache.org/r/11603
Stop tracker timer when we terminate tasks.

Review: https://reviews.apache.org/r/11604
Add --enable-debug configure flag.

Review: https://reviews.apache.org/r/11605
Increase slave timeout.

Review: https://reviews.apache.org/r/11606
Use XZ (LZMA) for package on Linuxes.

Review: https://reviews.apache.org/r/11112
Turn down noise from ZooKeeper.

Review: https://reviews.apache.org/r/11127
Fix hadoop 0.20.205.0 dist.

Review: https://reviews.apache.org/r/11662
WebUI: Use slave hostname rather than libprocess.

It's safer to use the hostname of the slave rather than the libprocess
IP since we don't necessarily know that the interface's IP is publicly
accessible.  This applies especially for services like EC2.

Review: https://reviews.apache.org/r/11813
Fix executor IDs in web UI.

Some frameworks don't report an executor ID, but have a task ID. As a
workaround, we can use the task ID when the executor ID is empty.

Review: https://reviews.apache.org/r/11814