ftp,dcap: Don't export child doors

This patch fixes a regression introduced in dCache 2.7.

Target: trunk
Request: 2.9
Request: 2.8
Request: 2.7
Require-notes: yes
Require-book: no
Acked-by: Albert Rossi <arossi@fnal.gov>
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/7005/
(cherry picked from commit eeb930158860212fcf3a9360641235fbd57c67b2)
Merge pull request #577 from gbehrmann/fix/2.8/rb7005

Fix/2.8/rb7005