support/download/svn: generate reproducible svn archives

To generate a reproducible archive from a svn repository mainly the same
aproach is done like for the archives from a git repository.

Signed-off-by: Heiko Thiery <heiko.thiery@gmail.com>
[yann.morin.1998@free.fr: get the date of the revision]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>