Added support for RHEL and did some syntax cleaning

Assume that "RedHat" also works where "CentOS" does.

mutt/manifests/init.pp

@@ -12,7 +12,7 @@ class mutt {
         $mail_domain = $domain
     }
 
-    case $operatingsystem {
+    case $::operatingsystem {
         openbsd: { $muttconfdir = "/etc/mutt/Muttrc" }
         default: { $muttconfdir = "/etc" }
     }
@@ -31,7 +31,7 @@ class mutt {
         content => template("mutt/Muttrc.local.erb"),
         mode    => "0644",
         owner   => "root",
-        group   => $operatingsystem ? {
+        group   => $::operatingsystem ? {
             openbsd => "wheel",
             default => "root",
         },

mutt/templates/Muttrc.local.erb

@@ -4,7 +4,7 @@ set use_8bitmime
 set hostname=<%= mail_domain %>
 
 set imap_authenticators="gssapi:plain"
-<% if operatingsystem = "CentOS" and operatingsystemrelease =~ /^6\./-%>
+<% if ['CentOS','RedHat'].index(operatingsystem) and operatingsystemrelease =~ /^6\./-%>
 set ssl_ca_certificates_file="/etc/pki/tls/certs/ca-bundle.crt"
 <% end -%>