Ignore SIGPIPE such that write returns EPIPE.

Currently a http server will be killed on receipt of SIGPIPE
if a client closes a socket which the server is trying to
write to.

R=rsc
APPROVED=rsc
DELTA=2  (0 added, 0 deleted, 2 changed)
OCL=27959
CL=28055

src/runtime/darwin/signals.h

@@ -21,7 +21,7 @@ static SigTab sigtab[] = {
 	/* 10 */	C, "SIGBUS: bus error",
 	/* 11 */	C, "SIGSEGV: segmentation violation",
 	/* 12 */	C, "SIGSYS: bad system call",
-	/* 13 */	0, "SIGPIPE: write to broken pipe",
+	/* 13 */	I, "SIGPIPE: write to broken pipe",
 	/* 14 */	0, "SIGALRM: alarm clock",
 	/* 15 */	0, "SIGTERM: termination",
 	/* 16 */	0, "SIGURG: urgent condition on socket",

src/runtime/linux/signals.h

@@ -21,7 +21,7 @@ static SigTab sigtab[] = {
 	/* 10 */	0, "SIGUSR1: user-defined signal 1",
 	/* 11 */	C, "SIGSEGV: segmentation violation",
 	/* 12 */	0, "SIGUSR2: user-defined signal 2",
-	/* 13 */	0, "SIGPIPE: write to broken pipe",
+	/* 13 */	I, "SIGPIPE: write to broken pipe",
 	/* 14 */	0, "SIGALRM: alarm clock",
 	/* 15 */	0, "SIGTERM: termination",
 	/* 16 */	0, "SIGSTKFLT: stack fault",