release.py: use a loop where appropriate.
release.py: use a loop where appropriate.

* tools/dist/release.py
  (RollDep, AutoconfDep, LibtoolDep, SwigDep): Update reference to self.label.
  (build_env): Iterate over the list of deps, rather than doing so manually.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion