Define new minor version of fasthadd, namely 2.1:

* the new minor version 2.1 is defined so that it is explicitly built on top of the new ROOT 6.0.6, featuring changes in the histogram serialisation;
* the code base has been moved to the latest 80X pre-release, but no changes in the source file is done.
No changes in performance observed or expected.

fasthadd.spec

@@ -1,8 +1,8 @@
-### RPM external fasthadd 2.0
+### RPM external fasthadd 2.1
 
 #Change the commit hash every time a new version is needed.
-#Commit mapped to merge of PR 10280
-%define commit 8db96f30b22860033087994689f4ec3bb024a268
+#Commit mapped to CMSSW_8_0_0_pre6
+%define commit 38304a4dbdfc1a5e7cc860afbb1c31dd09a9ff1e
 Source0: https://raw.githubusercontent.com/cms-sw/cmssw/%commit/DQMServices/Components/bin/fastHadd.cc
 Source1: https://raw.githubusercontent.com/cms-sw/cmssw/%commit/DQMServices/Core/src/ROOTFilePB.proto
 Requires: protobuf root