Fix NameError in _interpret_frame_flags.
Fix NameError in _interpret_frame_flags.

Fixes issue 35.
danielthesoto/stagger,Rose-Hawk/stagger,penfold1992/stagger,Rasor1911/stagger,Reroot/stagger,radec94/stagger,efth/stagger,SpaWnAge/stagger,manolomartinez/stagger,deNULL/stagger