Prevent plugins from running forever (Re: A basket of changes)

Maybe I've missed it in the flurry of patches, but I still see no sign of 
timeouts being enforced across plugins.

http://grokbase.com/p/perl/qpsmtpd/097nr0gyr2/never-times-out

http://www.nntp.perl.org/group/perl.qpsmtpd/2008/02/msg7779.html

Hanno once developed some code to address the issue, but I don't know what 
became of that.

http://grokbase.com/t/perl/qpsmtpd/0864wdzm0n/per-plugin-hook-timeouts