svnpubsub: be more careful when shelling out.

[in tools/server-side/svnpubsub]
* commit-hook.py
  (svnlook_uuid, svnlook_info, svnlook_changed):
* revprop-change-hook.py
  (svnlook_uuid, svnlook_revprop):
    Add an "--" end-of-arguments terminator, to escape REPOS_DIR and PROPNAME.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1486513 13f79535-47bb-0310-9956-ffa450edef68