Drop current version of Seitosh code. The contents are taken vom branch master
of [Seitosh](https://git.scc.kit.edu/Seitosh/Seitosh). The current master
commit in Seitosh is 8d7894a642.

Commands executed in the root directory of DENISE:

  rm -rfv contrib
  mkdir -pv contrib
  cp -vprd ~/git/Seitosh/src/libs/libaff contrib/aff
  cp -vprd ~/git/Seitosh/src/libs/libfourier contrib/fourier
  cp -vprd ~/git/Seitosh/src/libs/libseife contrib/libcseife
  cp -vprd ~/git/Seitosh/src/libs/libstfinv contrib/stfinv
  git add --force contrib

Since Seitosh on purpose does not provide export branches where source code
exports would be assembled in a hand-picked fashion, whole subdirectories from
Seitosh are simply copied. As a conseqeunce, the directory libcseife now also
contains Fortran code not really required by DENISE.

Replay vendor drop as took place in the original subversion repository of
DENISE. Source code from the subversion repository of TFSoftware was copied to
vendor branches aff, cseife, fourier, and stfinv.

aff:     subversion revision 372
cseife:  subversion revision 369
fourier: subversion revision 375
stfinv:  subversion revision 378

Source code is copied from tag directories 20130201

Notice: The contents of this commit are not in sync with the corresponding
export tags as present in the Seitosh repository. This must be due to
unintentional modification of files when copying contents as tagged for export
in TFSoftware to the vendor branch in the subversion repository of (formerly
called FWI_elastic/DENISE).