hook phase debugging must traverse to find line number

Extra logging was added in:

http://code.sixapart.com/trac/djabberd/changeset/799

This new logging makes calls to B::svref_2object, which is apparently some part of the perl compile that allows you to traverse the call stack and figure out who called you.

Example debug output:

For phase [PresenceCheck] invoking hook 1 of 2 defined at: lib/DJabberd/PresenceChecker.pm:26 

There seems to be a problem however in some cases.  I'm not exactly sure why.  But in some case:

$cv->ROOT->first->line

returns the correct line number

while:

$cv->ROOT->first->first->line

causes an error: (Can't locate object method "first" via package "B::COP")

Example callback of this case:

For phase [AlterPresenceAvailable] invoking hook 3 of 3 defined at: lib/DJabberd/VHost.pm:201


So, it seems that instead of blindly calling '$cv->ROOT->first->first->line', the code needs to traverse these B::LISTOP objects to the proper depth to find a B::COP object from which we can get the line number.