test cleanup
	- do not print tracebacks if $GOTRACEBACK=0
	- set GOTRACEBACK=0 during tests
	- filter out pc numbers in errors

R=r
DELTA=70  (22 added, 30 deleted, 18 changed)
OCL=15618
CL=15642
diff --git a/src/runtime/runtime.h b/src/runtime/runtime.h
index 04f1737..3d439ca 100644
--- a/src/runtime/runtime.h
+++ b/src/runtime/runtime.h
@@ -212,6 +212,7 @@
 void*	mal(uint32);
 uint32	cmpstring(string, string);
 void	initsig(void);
+int32	gotraceback(void);
 void	traceback(uint8 *pc, uint8 *sp, G* gp);
 void	tracebackothers(G*);
 int32	open(byte*, int32, ...);