How can turn off issue tracking in Testlink

[aostad]

I'm wondering how issue tracking system can be turned off in Testlink.

In case the bug tracking server is down, we need to turn off the feature, otherwise the execution page will be blank. In old version of Testlink, we could do it through configuration file and set the variable to NO (i think) to turn it off or turn it on by setting the variable to the name of bug tracker (e.g Mantis). How can we control it now?