Changes list priority from int to double.

This allows an easy implementation of something like A* in work queue,
while preserving the old int behaviour.
Expire tasks by end time, at the master
Add python binding
Mark expired completed tasks at worker
Expire running tasks at worker
Merge pull request #538 from btovar/expire_tasks_by_end_time

Expire tasks by end time
Merge pull request #559 from btovar/priority_double

Changes list priority from int to double.
If connection fails during auth, retry.

chirp_client_connect would treat any failure during authentication as EACCES
which would prevent chirp_reli from retrying. This caused the chirp tool to
fail for Anna/Charles in their experiments.

This commit also adds failure checking for all link calls.
If connection fails during auth, retry.

* chirp-auth-disconnect:
  If connection fails during auth, retry.