malloc bug fixes.

use malloc by default.
free stacks.

R=r
DELTA=424  (333 added, 29 deleted, 62 changed)
OCL=21553
CL=21584
diff --git a/src/runtime/runtime.h b/src/runtime/runtime.h
index a8d40f8..fc4e5ba 100644
--- a/src/runtime/runtime.h
+++ b/src/runtime/runtime.h
@@ -76,10 +76,6 @@
 	true	= 1,
 	false	= 0,
 };
-enum
-{
-	SmallFreeClasses = 168,	// number of small free lists in malloc
-};
 
 /*
  * structures
@@ -158,6 +154,7 @@
 	int32	siz1;
 	int32	siz2;
 	int32	id;
+	int32	mallocing;
 	Note	havenextg;
 	G*	nextg;
 	M*	schedlink;