STYLE: adjust globalIndex/CompactListList overflow reporting

- report location with previous good offset and the new count that
  would cause overflow. Simpler to report and the (very long) list
  of input sizes is not particularly useful for diagnostics either.

ENH: add globalIndex comparison operators

- for outputting lists of globalIndex

src/OpenFOAM/parallel/globalIndex/globalIndexTemplates.C

@@ -49,12 +49,14 @@ Foam::globalIndex::calcListOffsets
         label start = 0;
         for (label i = 0; i < len; ++i)
         {
+            const label count = lists[i].size();
+
             values[i] = start;
-            start += lists[i].size();
+            start += count;
 
             if (checkOverflow && start < values[i])
             {
-                reportOverflowAndExit(i);
+                reportOverflowAndExit(i, values[i], count);
             }
         }
         values[len] = start;
@@ -1005,12 +1007,12 @@ OutputContainer Foam::globalIndex::scatter
         // The globalIndex might be correct on master only,
         // so scatter local sizes to ensure consistency
 
-        const label localLen
+        const label count
         (
             UPstream::listScatterValues<label>(this->localSizes(), comm)
         );
 
-        OutputContainer localData(localLen);
+        OutputContainer localData(count);
         this->scatter(allData, localData, tag, commsType, comm);
 
         return localData;