* guix/svn-download.scm (subversion-package): New procedure. (svn-fetch): Use it. Remove 'svn-for-build'. Use a gexp and 'gexp->derivation'.
* guix/svn-download.scm, guix/build/svn.scm: New files. * Makefile.am (MODULES): Add them. Signed-off-by: Ludovic Courtès <ludo@gnu.org>