allow using the user's email address as a http parameter in gravatar urls for...

allow using the user's email address as a http parameter in gravatar urls for custom avatar systems. For example:
plain_url: "http://avatar.company.com/avatar/?mail=%{email}&size=%{size}"

add mention of the different placeholders possible for gravatar urls, mentionning the new %{email}

app/helpers/application_helper.rb

@@ -75,7 +75,7 @@ module ApplicationHelper
     else
       gravatar_url = request.ssl? || gitlab_config.https ? Gitlab.config.gravatar.ssl_url : Gitlab.config.gravatar.plain_url
       user_email.strip!
-      sprintf gravatar_url, hash: Digest::MD5.hexdigest(user_email.downcase), size: size
+      sprintf gravatar_url, hash: Digest::MD5.hexdigest(user_email.downcase), size: size, email: user_email
     end
   end
 

config/gitlab.yml.example

@@ -117,6 +117,7 @@ production: &base
   ## Gravatar
   gravatar:
     enabled: true                 # Use user avatar image from Gravatar.com (default: true)
+    # gravatar urls: possible placeholders: %{hash} %{size} %{email}
     # plain_url: "http://..."     # default: http://www.gravatar.com/avatar/%{hash}?s=%{size}&d=mm
     # ssl_url:   "https://..."    # default: https://secure.gravatar.com/avatar/%{hash}?s=%{size}&d=mm