[MCOL-4709] Disk-based aggregation

* Introduce multigeneration aggregation

* Do not save unused part of RGDatas to disk
* Add IO error explanation (strerror)

* Reduce memory usage while aggregating
* introduce in-memory generations to better memory utilization

* Try to limit the qty of buckets at a low limit

* Refactor disk aggregation a bit
* pass calculated hash into RowAggregation
* try to keep some RGData with free space in memory

* do not dump more than half of rowgroups to disk if generations are
  allowed, instead start a new generation
* for each thread shift the first processed bucket at each iteration,
  so the generations start more evenly

* Unify temp data location

* Explicitly create temp subdirectories
  whether disk aggregation/join are enabled or not

utils/configcpp/configcpp.h

@@ -203,6 +203,14 @@ public:
      */
     EXPORT const std::vector<std::string> enumSection(const std::string& section);
 
+    enum class TempDirPurpose
+    {
+      Joins,      ///< disk joins
+      Aggregates  ///< disk-based aggregation
+    };
+    /** @brief Return temporaru directory path for the specified purpose */
+    EXPORT std::string getTempFileDir(TempDirPurpose what);
+
 protected:
     /** @brief parse the XML file
     *