[api] Fix broken /source/remote_link:project/_meta in Rails2.3 due to…

… send_file streaming when not using use_xforward or x_rewrite_host in forward_from_backend

src/api/lib/opensuse/validator.rb

@@ -1,4 +1,5 @@
 require 'tempfile'
+require 'stringio'
 
 # This module encapsulates XML schema validation for individual controller actions.
 # It allows to verify incoming and outgoing XML data and to set different schemas based
@@ -52,7 +53,14 @@ def validate_xml_response
       opt[:method] = request.method.to_s
       opt[:type] = "response"
       if response.status.to_s == "200"
-        Suse::Validator.validate(opt, response.body.to_s)
+        if response.body.respond_to? :call
+          sio = StringIO.new()
+          response.body.call(nil, sio) # send_file can return a block that takes |response, output|                       
+          str = sio.string
+        else
+          str = response.body.to_s
+        end
+        Suse::Validator.validate(opt, str)
       end
     end