Always give hashlib.sha1 and friends bytes.

This fixes an experienced bug where you couldn't subscribe to a stream
with non-ASCII characters (failing with a UnicodeEncodeError), as well
as many other potential bugs.

(imported from commit f084a4b4b597b85935655097a7b5a163811c4d71)

zephyr/lib/utils.py

@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+import hashlib
 from time import sleep
 
 # Runs the callback with slices of all_list of a given batch_size
@@ -21,3 +22,11 @@ def run_in_batches(all_list, batch_size, callback, sleep_time = 0, logger = None
 
         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()