Added RedHat/CentOS support to postfix cookbook

Signed-off-by: jtimberman <joshua@opscode.com>

recipes/default.rb

@@ -22,8 +22,24 @@ package "postfix" do
   action :install
 end
 
-service "postfix" do
-  action :enable
+case node[:platform]
+when "ubuntu", "debian" 
+  service "postfix" do
+   action :enable
+  end
+when "redhat", "centos"
+  service "postfix" do
+    action :nothing
+  end
+  service "sendmail" do
+    action :nothing
+  end
+  execute "switch_mailer_to_postfix" do
+    command "/usr/sbin/alternatives --set mta /usr/sbin/sendmail.postfix"
+    notifies :stop, resources(:service => "sendmail")
+    notifies :start, resources(:service => "postfix")
+    not_if "/usr/bin/test /etc/alternatives/mta -ef /usr/sbin/sendmail.postfix"
+  end
 end
 
 %w{main master}.each do |cfg|