Moved KidIdentifier to globals to make pinger happy.

Moved KidIdentifier to globals to make pinger happy.

Pinger and possibly other optional externals require KidIdentifier via
debugs(). Instead of making KidIdentifier global, we could add a "plugin" API
to add program-dependent stuff to debugs() and friends, but we should not add
that kind of complexity unless really necessary. We could also link pinger
with libipc.la but that will probably cause more problems with IPC
dependencies.