diffPoolFiles: Add option to compare both mem-size and disk-size

This relates to https://its.cern.ch/jira/browse/ATEAM-596

I just learned that diffPoolFile never did what I thought it does: Checking both the compressed and the uncompressed size of containers. With this MR, I am adding this as an option (--strict) that is off by default.

Running with that option on an ESD files that is supposed to be identical, I get:

================================================================================
::: Comparing POOL files...
 ref : ../Feb18/q431_1/myESD.pool.root
 chk : ../Feb18/q431_2/myESD.pool.root
--------------------------------------------------------------------------------
::: comparing common content (mem-size / disk-size)...
[ERR]        2.157 /        1.184 kb (ref) ==>        2.157 /        1.199 kb (chk) | RecoTimingObj_p1_RAWtoESD_mems
[ERR]        1.607 /        0.972 kb (ref) ==>        1.607 /        0.976 kb (chk) | RecoTimingObj_p1_RAWtoESD_timings
[ERR]     1608.476 /      286.969 kb (ref) ==>     1608.476 /      286.953 kb (chk) | Trk::SegmentCollection_tlp4_MuonSegments
[ERR]      552.057 /      122.162 kb (ref) ==>      552.057 /      122.154 kb (chk) | Trk::TrackCollection_tlp6_MuonSpectrometerTracks

The timing-difference is no surprise, the Muon-stuff probably a remaining reproducibility that we haven't caught with the coarse tests we are doing now.

Tagging @amete and @gemmeren ....