celery: upgrade to Celery 3

Celery 3 is more than 2 and is the future and should be more stable than Celery 2.

There might be problems like
  PRECONDITION_FAILED - cannot redeclare exchange 'celeryresults' in vhost 'kallithea' with different type, durable, internal or autodelete value
when celery is upgraded and it tries to upgrade existing tasks.

One way to avoid that problem:
- make sure celery has run to completion and there are no important pending tasks,
- delete the old vhost,
- upgrade celery,
- create new vhost
- set permissions for vhost
- profit

kallithea/lib/celerypylons/__init__.py

@@ -33,4 +33,4 b" os.environ['CELERY_LOADER'] = CELERYPYLO"
 import celery.app as app
 import celery.result as result
 from celery.task import task
-from celery.bin import celeryd
+from celery.bin import worker

kallithea/lib/paster_commands/celeryd.py

@@ -24,7 +24,7 b' class Command(BasePasterCommand):'
 
     def update_parser(self):
         from kallithea.lib import celerypylons
-        cmd = celerypylons.celeryd.WorkerCommand(celerypylons.app.app_or_default())
+        cmd = celerypylons.worker.worker(celerypylons.app.app_or_default())
         for x in cmd.get_options():
             self.parser.add_option(x)
 
@@ -42,5 +42,5 b' class Command(BasePasterCommand):'
         kallithea.CELERY_ON = CELERY_ON
 
         load_rcextensions(config['here'])
-        cmd = celerypylons.celeryd.WorkerCommand(celerypylons.app.app_or_default())
+        cmd = celerypylons.worker.worker(celerypylons.app.app_or_default())
         return cmd.run(**vars(self.options))

setup.py

@@ -47,7 +47,7 b' requirements = ['
     "Mako>=0.9.0,<=1.0.0",
     "pygments>=1.5",
     "whoosh>=2.4.0,<=2.5.7",
-    "celery>=2.2.5,<2.3",
+    "celery>=3.1,<3.2",
     "babel>=0.9.6,<=1.3",
     "python-dateutil>=1.5.0,<2.0.0",
     "markdown==2.2.1",