FairSoft release mar15 was re-tagged

Unfortunately we had to re-tag the release one day after the release.
We had to re-tag the FairSoft release mar15.
This was needed because some tar archive was removed from the dowload server of the upstream project.

If you already have downloaded the previous version and you don't want to build the python bindings for
Geant4 and Root there is no problem and you can stay with the old version of the release.

If you want to build these bindings using the old version of the release you will encounter an error when the
build procedure tries to unpack the xerces-c tar archive.
In this case you have to get the new re-tagged version of the mar15 release.

If you got the wrong tag, and want the new one, please delete
the old one in your local working directory and fetch the new one by doing:

git tag -d mar15
git fetch origin tag mar15

to get my updated tag.

You can test which tag you have by doing

git rev-parse mar15

which should return 5e3fc65a2fbee3c6aa... if you have the new version.

Sorry for the inconvenience.