Add the workers connection to _connection_stack

This allows jobs to use get_current_connection() with a resolvable connection.
And then these jobs can schedule new jobs for example (my use-case). Or attach
information to their job-object.

Also pop the pushed connection after running the jobs. This is needed for some
tests that check the _connection_stack afterwards;-) And also for use-cases
where the workers are used multiple times.

fixes nvie/rq#479

rq/worker.py

@@ -16,7 +16,7 @@ from datetime import timedelta
 
 from rq.compat import as_text, string_types, text_type
 
-from .connections import get_current_connection
+from .connections import get_current_connection, push_connection, pop_connection
 from .defaults import DEFAULT_RESULT_TTL, DEFAULT_WORKER_TTL
 from .exceptions import DequeueTimeout
 from .job import Job, JobStatus
@@ -581,6 +581,9 @@ class Worker(object):
         self.prepare_job_execution(job)
 
         with self.connection._pipeline() as pipeline:
+
+            push_connection(self.connection)
+
             started_job_registry = StartedJobRegistry(job.origin, self.connection)
 
             try:
@@ -623,6 +626,9 @@ class Worker(object):
                 self.handle_exception(job, *sys.exc_info())
                 return False
 
+            finally:
+                pop_connection()
+
         self.log.info('{0}: {1} ({2})'.format(green(job.origin), blue('Job OK'), job.id))
         if rv is not None:
             log_result = "{0!r}".format(as_text(text_type(rv)))