Nack multipart SMSes with more than 255 parts.

[hodgestar]

Currently attempting to send really long SMSes results in:

Stacktrace (most recent call last):

  File "twisted/internet/defer.py", line 1097, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File "twisted/python/failure.py", line 389, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
  File "vumi/transports/smpp/smpp_transport.py", line 394, in handle_outbound_message
    message, protocol)
  File "twisted/internet/defer.py", line 1097, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File "twisted/python/failure.py", line 389, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
  File "vumi/transports/smpp/processors/mica.py", line 168, in handle_outbound_message
    optional_parameters=optional_parameters,
  File "twisted/internet/defer.py", line 1099, in _inlineCallbacks
    result = g.send(result)
  File "vumi/transports/smpp/protocol.py", line 626, in submit_csm_udh
    chr(len(split_msg)),

ValueError: chr() arg not in range(256)

The SMPP protocol doesn't allow sending messages with more than 255 parts, but we should log and nack such messages instead of raising an exception.

[hodgestar]

Just noting that we're still seeing this in production from time to time:

File "/var/praekelt/vumi-go/ve/src/vumi/vumi/transports/smpp/processors/mica.py", line 190, in handle_outbound_message
            optional_parameters=optional_parameters,
File "/var/praekelt/vumi-go/ve/local/lib/python2.7/site-packages/twisted/internet/defer.py", line 1099, in _inlineCallbacks
            result = g.send(result)
File "/var/praekelt/vumi-go/ve/src/vumi/vumi/transports/smpp/protocol.py", line 642, in submit_csm_udh
            chr(len(split_msg)),
        exceptions.ValueError: chr() arg not in range(256)