fmbtgti: fix memory releasing in visual logging
fmbtgti: fix memory releasing in visual logging

Python garbage collector needed help due to a cyclical reference where
an object has user-defined destructor.

OMKR/fMBT,yoonkiss/fMBT,giantpinkwalrus/fMBT,01org/fMBT,heivi/fMBT,yoonkiss/fMBT,OMKR/fMBT,pablovirolainen/fMBT,mixu-/fMBT,giantpinkwalrus/fMBT,01org/fMBT,mlq/fMBT,mlq/fMBT,acozzette/fMBT,violep01/fMBT,pyykkis/fMBT,pablovirolainen/fMBT,pombreda/fMBT,pyykkis/fMBT,pyykkis/fMBT,mixu-/fMBT,rseymour/fMBT,violep01/fMBT,mixu-/fMBT,heivi/fMBT,yoonkiss/fMBT,rseymour/fMBT,pombreda/fMBT,acozzette/fMBT,OMKR/fMBT,violep01/fMBT,yoonkiss/fMBT,rseymour/fMBT,acozzette/fMBT,acozzette/fMBT,mlq/fMBT,rseymour/fMBT,pombreda/fMBT,01org/fMBT,mlq/fMBT,mlq/fMBT,pyykkis/fMBT,01org/fMBT,pombreda/fMBT,pablovirolainen/fMBT,mixu-/fMBT,pyykkis/fMBT,acozzette/fMBT,pombreda/fMBT,violep01/fMBT,giantpinkwalrus/fMBT,OMKR/fMBT,pablovirolainen/fMBT,rseymour/fMBT,rseymour/fMBT,heivi/fMBT,pyykkis/fMBT,violep01/fMBT,pombreda/fMBT,giantpinkwalrus/fMBT,OMKR/fMBT,01org/fMBT,OMKR/fMBT,giantpinkwalrus/fMBT,heivi/fMBT,mixu-/fMBT,yoonkiss/fMBT,rseymour/fMBT,mlq/fMBT,pombreda/fMBT,heivi/fMBT,heivi/fMBT,pablovirolainen/fMBT,heivi/fMBT,pablovirolainen/fMBT,mlq/fMBT