Revert "Revert "Implement TH1::Clone""

This reverts commit 9b16f29d5d52c7da4ff6079886db5d21959ac33a.
Always delete the array when the array size goes down to zero.

This fixes a problem seen by CMS when using TH1::Copy on histograms read
from a TTree.

This amend commit d31f38f98c66af492c20c3bf060df13d64c465f0 (circa 2005)
Make previous commit work with 5.34.18

The previous commit to this file only worked with newer versions of
ROOT. This modification makes it work with 5.34.18.
Merge pull request #46 from Dr15Jones/philippeFixEmptyArrayIO

Philippe's fix for empty array I/O