acid bug fix.

lock printf output to avoid interlacing debug prints.

R=r
DELTA=10  (7 added, 0 deleted, 3 changed)
OCL=35539
CL=35561

src/pkg/runtime/print.c

@@ -4,6 +4,7 @@
 
 #include "runtime.h"
 
+static Lock debuglock;
 
 void
 dump(byte *p, int32 n)
@@ -36,6 +37,8 @@ printf(int8 *s, ...)
 	int8 *p, *lp;
 	byte *arg, *narg;
 
+	lock(&debuglock);
+
 	lp = p = s;
 	arg = (byte*)(&s+1);
 	for(; *p; p++) {
@@ -96,6 +99,8 @@ printf(int8 *s, ...)
 	}
 	if(p > lp)
 		write(1, lp, p-lp);
+
+	unlock(&debuglock);
 }