class TTableMap: public TObject

 TTableMap class is helper class to keep the list of the referencs to the
 TTable rows and iterate over it.
 TTableMap is a persistent class.
 The pointer to the TTableMap object may be used as an element
 of the TTable row and saved with the table all together.

 For example, the track table may contain a member to the "map" of the hits
  struct {
    float helix;
    TTableMap *hits;
  } tracks_t;

   // Create track table:
   LArTrackTable *tracks = new LArTrackTable(...);

   // Get pointer to the hit table
   LArHitTable *hits = GiveMeHits();
   // Loop over all tracks
   LArTrackTable::iterator track = tracks->begin();
   LArTrackTable::iterator last = tracks->end();
   for (;track != last;track++) {
     // Find all hits of this track
      LArHitTable::iterator hit     = hits->begin();
      LArHitTable::iterator lastHit = hits->end();
      Long_t hitIndx = 0;
      // Create an empty list of this track hits
      (*track).hits = new TTableMap(hits);
      for(;hit != lastHit;hit++,hitIndx) {
        if (IsMyHit(*hit)) {  // add this hit index to the current track
           (*track).hits->push_back(hitIndx);
        }
      }
   }