seq: use stdout.write_all() instead of print!()

Change from using `print!()` to using `stdout.write_all()` in order to
allow the main function to handle broken pipe errors gracefully.

tests/by-util/test_seq.rs

@@ -1,4 +1,5 @@
 use crate::common::util::*;
+use std::io::Read;
 
 #[test]
 fn test_rejects_nan() {
@@ -176,3 +177,26 @@ fn test_width_negative_zero() {
         .stdout_is("-0\n01\n")
         .no_stderr();
 }
+
+// TODO This is duplicated from `test_yes.rs`; refactor them.
+/// Run `seq`, capture some of the output, close the pipe, and verify it.
+fn run(args: &[&str], expected: &[u8]) {
+    let mut cmd = new_ucmd!();
+    let mut child = cmd.args(args).run_no_wait();
+    let mut stdout = child.stdout.take().unwrap();
+    let mut buf = vec![0; expected.len()];
+    stdout.read_exact(&mut buf).unwrap();
+    drop(stdout);
+    assert!(child.wait().unwrap().success());
+    assert_eq!(buf.as_slice(), expected);
+}
+
+#[test]
+fn test_neg_inf() {
+    run(&["--", "-inf", "0"], b"-inf\n-inf\n-inf\n");
+}
+
+#[test]
+fn test_inf() {
+    run(&["inf"], b"1\n2\n3\n");
+}