/usr/local/bin might not exist so use /usr/bin in the chdir test.

R=rsc
DELTA=1  (0 added, 0 deleted, 1 changed)
OCL=31708
CL=31713

src/pkg/os/os_test.go

@@ -466,7 +466,7 @@ func TestChdirAndGetwd(t *testing.T) {
 	}
 	// These are chosen carefully not to be symlinks on a Mac
 	// (unlike, say, /var, /etc, and /tmp).
-	dirs := []string{ "/bin", "/", "/usr/local/bin" };
+	dirs := []string{ "/bin", "/", "/usr/bin" };
 	for mode := 0; mode < 2; mode++ {
 		for i, d := range dirs {
 			if mode == 0 {