os: make the system info a value not a pointer on unix
fix a couple of other minor related details.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5690071
diff --git a/src/pkg/os/exec_unix.go b/src/pkg/os/exec_unix.go
index e5905f0..8d000e9 100644
--- a/src/pkg/os/exec_unix.go
+++ b/src/pkg/os/exec_unix.go
@@ -30,7 +30,7 @@
 	}
 	ps = &ProcessState{
 		pid:    pid1,
-		status: &status,
+		status: status,
 		rusage: &rusage,
 	}
 	return ps, nil