[manual] Rename Django app from zephyr to zerver.

This needs to be deployed to both staging and prod at the same
off-peak time (and the schema migration run).

At the time it is deployed, we need to make a few changes directly in
the database:

(1) UPDATE django_content_type set app_label='zerver' where app_label='zephyr';
(2) UPDATE south_migrationhistory set app_name='zerver' where app_name='zephyr';

(imported from commit eb3fd719571740189514ef0b884738cb30df1320)

zerver/lib/utils.py

@@ -0,0 +1,95 @@
+# -*- coding: utf-8 -*-
+from __future__ import absolute_import
+
+import hashlib
+from time import sleep
+from django.conf import settings
+
+def statsd_key(val, clean_periods=False):
+    if not isinstance(val, str):
+        val = str(val)
+
+    if ':' in val:
+        val = val.split(':')[0]
+    val = val.replace('-', "_")
+    if clean_periods:
+        val = val.replace('.', '_')
+
+    return val
+
+class StatsDWrapper(object):
+    """Transparently either submit metrics to statsd
+    or do nothing without erroring out"""
+
+    # Backported support for gauge deltas
+    # as our statsd server supports them but supporting
+    # pystatsd is not released yet
+    def _our_gauge(self, stat, value, rate=1, delta=False):
+            """Set a gauge value."""
+            from django_statsd.clients import statsd
+            if delta:
+                value = '%+g|g' % (value,)
+            else:
+                value = '%g|g' % (value,)
+            statsd._send(stat, value, rate)
+
+    def __getattr__(self, name):
+        # Hand off to statsd if we have it enabled
+        # otherwise do nothing
+        if name in ['timer', 'timing', 'incr', 'decr', 'gauge']:
+            if settings.USING_STATSD:
+                from django_statsd.clients import statsd
+                if name == 'gauge':
+                    return self._our_gauge
+                else:
+                    return getattr(statsd, name)
+            else:
+                return lambda *args, **kwargs: None
+
+        raise AttributeError
+
+statsd = StatsDWrapper()
+
+# Runs the callback with slices of all_list of a given batch_size
+def run_in_batches(all_list, batch_size, callback, sleep_time = 0, logger = None):
+    if len(all_list) == 0:
+        return
+
+    limit = (len(all_list) / batch_size) + 1;
+    for i in xrange(limit):
+        start = i*batch_size
+        end = (i+1) * batch_size
+        if end >= len(all_list):
+            end = len(all_list)
+        batch = all_list[start:end]
+
+        if logger:
+            logger("Executing %s in batch %s of %s" % (end-start, i+1, limit))
+
+        callback(batch)
+
+        if i != limit - 1:
+            sleep(sleep_time)
+
+def make_safe_digest(string, hash_func=hashlib.sha1):
+    """
+    return a hex digest of `string`.
+    """
+    # hashlib.sha1, md5, etc. expect bytes, so non-ASCII strings must
+    # be encoded.
+    return hash_func(string.encode('utf-8')).hexdigest()
+
+
+def log_statsd_event(name):
+    """
+    Sends a single event to statsd with the desired name and the current timestamp
+
+    This can be used to provide vertical lines in generated graphs,
+    for example when doing a prod deploy, bankruptcy request, or
+    other one-off events
+
+    Note that to draw this event as a vertical line in graphite
+    you can use the drawAsInfinite() command
+    """
+    event_name = "events.%s" % (name,)
+    statsd.incr(event_name)