Generate a SOAP header as defined in:
    http://www.salesforce.com/us/developer/docs/api/Content/soap_headers.htm

def generateHeader(self, sObjectType):
    '''
    Generate a SOAP header as defined in:
    http://www.salesforce.com/us/developer/docs/api/Content/soap_headers.htm
    '''
    try:
      return self._sforce.factory.create(sObjectType)
    except:
      print 'There is not a SOAP header of type %s' % sObjectType