Resque::Worker#pid on remote workers via Resque::Worker::find

Se #857.

1. Exceptions in the appropriate test were getting "handled" by the
   worker's block handler, causing failed assertions to be muted.
   Fixes the test.

2. Since we have access to the pid when creating a Worker object
   from Resque::Worker::find, set the pid appropriately.
Add test for finding other workers
update changelog
Merge pull request #1156 from resque/issue-857/set-pid-in-worker-find

Resque::Worker#pid on remote workers via Resque::Worker::find; fixes #857