Add support to remove a prefix from leaves in diff-root. This is useful to comparing files which might change the output container names for special cases (e.g. pile-up premixing).
Example command:
acmd.py diff-root mc16d_premixing.RDO.pool.root mc16d_premixing_MT.RDO.pool.root --entries 1 --leaves-prefix Bkg_ --ignore-leaves RecoTimingObj_p1_HITStoRDO_timings.timings index_ref/cc @jchapman