Generate consistent gravatar hash values as per documentation.

The gravatar documentation on implementing the hash specifies that leading
and trailing whitespace must be trimmed and all characters should be forced
to lowercase.
Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>

app/helpers/application_helper.rb

@@ -3,7 +3,8 @@ module ApplicationHelper
 
   def gravatar_icon(user_email, size = 40)
     gravatar_host = request.ssl? ? "https://secure.gravatar.com" :  "http://www.gravatar.com"
-    "#{gravatar_host}/avatar/#{Digest::MD5.hexdigest(user_email)}?s=#{size}&d=identicon"
+    user_email.strip!
+    "#{gravatar_host}/avatar/#{Digest::MD5.hexdigest(user_email.downcase)}?s=#{size}&d=identicon"
   end
 
   def fixed_mode?