Bug#343457: boot_xconf: syntax error in 'let LENGTH=($LENGTH - 1)'

[Petter Reinholdtsen <pere@hungry.com>]

Package: debian-edu-config
Version: 0.399
Severity: important

When upgrading debian-edu-config, I get this message from postinst.
This did not break the installation of the new package, so I set
severity only to important.

  Installing new version of config file /etc/init.d/update-hostname ...
  Installing new version of config file /etc/init.d/start-wlan ...
  Installing new version of config file /etc/init.d/report-reboot ...
  /etc/init.d/boot_xconf: line 43: syntax error near unexpected token `('
  /etc/init.d/boot_xconf: line 43: `      let LENGTH=($LENGTH - 1)'
  invoke-rc.d: initscript boot_xconf, action "start" failed.

This looks like a typo in the script.  I assume the code should
subtract 1 from the value of LENGTH.  Perhaps a posix shell compliant
notation should be used instead?