Now I stuble into my next problem. The FFTW extension does not exist.
Thus I have downloaded the package from
http://www.fftw.org/download.html.
The usual steps are
./configure
make
make install
This works like a charm, resulting without error.
But now I miss e.g. /usr/local/lib/libfftw.so whereas libfftw.a exists in this folder.
As FFTW is a huge package I don't know where to search.
So two questions come up:
1. how to get the missed .so-files?
2. how to get FFTW (or other software) permanently installed? Is it necessary to create a tcz and how to do this? The wiki seems to be down.