[cmake,release] autogenerate cmake package configuration files, if possible.

As Ansgar not the CMake package configuration files are quite generic. This
patch autogenerates them if their templates do not exist in the source tree.
In addition duneproject and am2cmake do not generate the templates as files
in the source tree anymore.
[autotools,bugfix] Fixes documentation building in tarballs.

When unpacking the tarballs, the time stamps are preserved, but the
access time of the files might be set differently. In addition during
configure Doxyfile is always created. This resulted in some files being
newer than the doxygen-tag in the tarball and triggered building the
documentation. This patch fixes the problem for me by only checking the
modification time and excluding Doxyfile.