Update issue tracker link in contributing guide.
STREAMING-50: Support transform workaround in JavaPairDStream

This ports a useful workaround (the `transform` function) to
JavaPairDStream. It is necessary to do things like sorting which
are not supported yet in the core streaming API.
include jobid in Executor commandline args
Merge pull request #461 from JoshRosen/fix/issue-tracker-link

Update issue tracker link in contributing guide
use appid instead of frameworkid; simplify stupid condition
Merge pull request #466 from pwendell/java-stream-transform

STREAMING-50: Support transform workaround in JavaPairDStream
Merge pull request #467 from squito/executor_job_id

include jobid in Executor commandline args