Resolves naming conflicts in partial files in hadd

Appends the same unique identifier to the name of the partial files
within the same hadd execution.

Author: xvallspl

main/src/hadd.cxx

@@ -79,6 +79,7 @@
 #include "Riostream.h"
 #include "TClass.h"
 #include "TSystem.h"
+#include "TUUID.h"
 #include "ROOT/StringConv.hxx"
 #include <stdlib.h>
 #include <climits>
@@ -405,9 +406,11 @@ int main( int argc, char **argv )
    std::vector<std::string> partialFiles;
 
    if (multiproc) {
+      auto uuid = TUUID();
+      auto partialTail = uuid.AsString(); 
       for (auto i = 0; (i * step) < filesToProcess; i++) {
          std::stringstream buffer;
-         buffer << "partial" << i << ".root";
+         buffer << "partial" << i <<"_"<< partialTail << ".root";
          partialFiles.emplace_back(buffer.str());
       }
    }
@@ -497,7 +500,7 @@ int main( int argc, char **argv )
    } else {
       status = sequentialMerge(fileMerger, ffirst, filesToProcess);
    }
-
+   
    if (status) {
       if (verbosity == 1) {
          std::cout << "hadd merged " << fileMerger.GetMergeList()->GetEntries() << " input files in " << targetname