When hud_used is deleted, references to those objects are removed, hence they are garbage collected.
Removed some code from metroids which could possible delete global_hud objects which would cause problems.
Added a verb to code/WorkInProgress/carn/debug_locnull.dm which prints all atoms with loc==null to world.log
git-svn-id: http://tgstation13.googlecode.com/svn/trunk@4774 316c924e-a436-60f5-8080-3fe189b3f50e
