Description of problem:

Some exceptions thrown from the ruby-qpid client code violate the API definition for Exception in Ruby.

http://ruby-doc.org/core/classes/Exception.html#M000683

Instead of a String, the message is an Array. This can cause a cascading failure in code that attempts to rescue an exception and uses the message in a context requiring a String.

>> begin
?> send_a_message_that_thows_exception
>> rescue => e
>> puts "oops, a problem: " + e.message
>> end
TypeError: can't convert Array into String
	from (irb):54:in `+'
	from (irb):54
>> p e.message.class
Array
>> p e.class
Qpid::Session::Exception
>> p e.message
[#<struct Struct::Qpid_Execution_exception error_code=403, command_id=#<Qpid::Serial:0x7fa4fc69fc78 @value=0>, class_code=0, command_code=0, field_index=0, description="unauthorized-access: someone cannot publish to some.topic with routing-key tmp.foo (qpid/broker/SemanticState.cpp:483)", error_info={}, st_type=execution_exception, id=#<Qpid::Serial:0x7fa4fc6aaba0 @value=0>>]

Occurs within Session.sync

ruby-qpid-0.7.946106-2.el6.x86_64 session.rb line 116-118:
     if error?
        raise Qpid::Session::Exception, @exceptions
      end