Changed localProperties to use ThreadLocal (not DynamicVariable).

The fact that DynamicVariable uses an InheritableThreadLocal
can cause problems where the properties end up being shared
across threads in certain circumstances.
Updated Spark on Mesos documentation.
More updates to Spark on Mesos documentation.
Merge pull request #927 from benh/mesos-docs

Updated Spark on Mesos documentation.
Merge pull request #926 from kayousterhout/dynamic

Changed localProperties to use ThreadLocal (not DynamicVariable).
Add git scm url for publishing
Merge remote-tracking branch 'upstream/master'