- Fix /etc/init.d/plc to have command usage show up on the tty rather

- Fix /etc/init.d/plc to have command usage show up on the tty rather
  than the log file

- Fix db-config to be a bit more cautious when
  /etc/planetlab/db-config.d doesn't exist

- Clean up db-config approach to ignore .bak, *~, .rpm{save,new}, and
  .orig files.

- Refactor generic plc-config-tty code into plc_config.py.
  plc-config-tty now contains MyPLC specific paths, "usual" variables,
  and the list of validated variables and the corresponding
  validator() function. This refactoring lets one reuse plc_config.py
  as a generic cmdline configuration tool for highly customer MyPLC
  like software.

Tagging module MyPLC - MyPLC-4.3-15