Update hadd and TFileMerger so that they prefix all their information message

with their names (when running hadd, the TFileMerger message are prefixed by hadd):

$ hadd -v 0 -f output.root input1.root input2.root 
$ hadd -v 1 -f output.root input1.root input2.root 
hadd merged 2 input files in output.root.
$ hadd -v 2 -f output.root input1.root input2.root 
hadd target file: output.root
hadd Source file 1: input1.root
hadd Source file 2: input2.root
hadd Target path: output.root:/


git-svn-id: http://root.cern.ch/svn/root/trunk@41444 27541ba8-7e3a-0410-8455-c3a389f83636