TODO:
  * Calculate "Installed-Size" field values.
  * Fix handling of optional control fields.
  * Fix oh-strip.
  * Make oh-strip obey a missing '-l' option.
  * Handle "Architecture" field in oh-gencontrol, opkbuild, and oh-buildopk.
  * Check on file ownership and modes.
  * Finish tar archive handling in opkhelper.