In class EWCorrectionWeight, use the name of one of the files from the
input data set to guess the physics content of the sample. This is a
change from using the path to the catalog file for the same purpose,
which is a change mistakenly introduced in commit [1]. Using the path to
the catalog file is a bug because the catalog is renamed simply to
"theLocalData.txt" when running with a local copy of input files (see
script Tools/prepareAllJobs.py).

[1] 60eb8ab6