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/avatar.py

@@ -1,5 +1,11 @@
 import hashlib
+from utils import make_safe_digest
 
 def gravatar_hash(email):
     """Compute the Gravatar hash for an email address."""
-    return hashlib.md5(email.lower()).hexdigest()
+    # Non-ASCII characters aren't permitted by the currently active e-mail
+    # RFCs. However, the IETF has published https://tools.ietf.org/html/rfc4952,
+    # outlining internationalization of email addresses, and regardless if we
+    # typo an address or someone manages to give us a non-ASCII address, let's
+    # not error out on it.
+    return make_safe_digest(email.lower(), hashlib.md5)