portfetch.tcl: Depend on port:subversion on 10.11 and earlier
portfetch.tcl: Depend on port:subversion on 10.11 and earlier

See: https://trac.macports.org/ticket/55933

danchr/macports-base,neverpanic/macports-base,neverpanic/macports-base,macports/macports-base,danchr/macports-base,macports/macports-base