Add GC_stop_world_external and GC_start_world_external that properly disable signals and acquire GC locks before calling GC_stop_world and GC_start_world respectively. Use these new functions external of GC in liveness code. May fix case 530367.

Conflicts:
	libgc/misc.c
Add dummy build_runtime_qnx.sh to build correctly in TC.
Merge pull request #54 from Unity-Technologies/unity-4.1-staging

Unity 4.1 - liveness fix (case 530367) and build fix for TC