seq(1): Put separator only between the elements.

- Using non-default ('\n') separator will produce an output with the
  separator at the end of the output, eg.

	% echo "[$(seq -s ' ' 0 2)]"
	[0 1 2 ]

- The output should always be followed by a new line character. Currently:

	% seq -s ' ' 0 2
	0 1 2 %

This change makes seq(1) to behave the same way Linux seq(1):

	% echo "[$(seq -s ' ' 0 2)]"
	[0 1 2]

	% seq -s ' ' 0 2
	0 1 2
	%

Approved by:	oshogbo
Differential Revision:	https://reviews.freebsd.org/D43094

usr.bin/seq/seq.c

@@ -181,8 +181,9 @@ main(int argc, char *argv[])
 
 	for (step = 1, cur = first; incr > 0 ? cur <= last : cur >= last;
 	    cur = first + incr * step++) {
+		if (step > 1)
+			fputs(sep, stdout);
 		printf(fmt, cur);
-		fputs(sep, stdout);
 		prev = cur;
 	}
 
@@ -202,15 +203,19 @@ main(int argc, char *argv[])
 	}
 	if (strcmp(cur_print, last_print) == 0 &&
 	    strcmp(cur_print, prev_print) != 0) {
-		fputs(last_print, stdout);
 		fputs(sep, stdout);
+		fputs(last_print, stdout);
 	}
 	free(cur_print);
 	free(last_print);
 	free(prev_print);
 
-	if (term != NULL)
+	if (term != NULL) {
+		fputs(sep, stdout);
 		fputs(term, stdout);
+	}
+
+	fputs("\n", stdout);
 
 	return (0);
 }