MultiChannel class support for arbitrary structures

[sveseli]

At this time MultiChannel class seems to support only those structures that have the top level "value" field, e.g.:

void PvaClientNTMultiData::setStructure(StructureConstPtr const &
structure,size_t index)
{
      FieldConstPtr field = structure->getField("value");
      if(!field) {
          string message = "channel "
             + pvaClientChannelArray[index]->getChannel()->getChannelName()
             + " does not have top level value field";
          throw std::runtime_error(message);
      }
}

This restriction should be removed in order to make this class useful for arbitrary structures (i.e., those that do not have top level "value" field).

[mrkraimer]

With latest pvaClientCPP PvaClienNTtMultiData, PvaClientNTMultiGet, and PvaClientNTMultiMonitor now work for data in addition to top level field named "value". In exampleCPP/exampleClient there are two new examples: ntMultiGet and ntMultiMonitor. These can be used to test. I have not looked at PvaClientNTMultiPut

[mrkraimer]

fixed with merge request #60