Use strtonum(3) for -t seconds, improve errors on invalid number input

Base 10 suffices, negative numbers should be invalid (not converted) and
zero not treated specially.

This also unifies error messages and removes unnecessary EINVAL from them
since strtonum()'s errstr is explicit enough already.

Feedback and OK martjin, tb

usr.sbin/apmd/apmd.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: apmd.c,v 1.82 2018/11/30 18:05:31 tedu Exp $	*/
+/*	$OpenBSD: apmd.c,v 1.83 2018/12/01 23:35:59 kn Exp $	*/
 
 /*
  *  Copyright (c) 1995, 1996 John T. Kohl
@@ -392,9 +392,10 @@ main(int argc, char *argv[])
 			sockname = optarg;
 			break;
 		case 't':
-			ts.tv_sec = strtoul(optarg, NULL, 0);
-			if (ts.tv_sec == 0)
-				usage();
+			ts.tv_sec = strtonum(optarg, 1, LLONG_MAX, &errstr);
+			if (errstr != NULL)
+				errx(1, "number of seconds is %s: %s", errstr,
+				    optarg);
 			break;
 		case 's':	/* status only */
 			statonly = 1;
@@ -422,14 +423,14 @@ main(int argc, char *argv[])
 			autoaction = AUTO_HIBERNATE;
 			autolimit = strtonum(optarg, 1, 100, &errstr);
 			if (errstr != NULL)
-				errc(1, EINVAL, "%s percentage: %s", errstr,
+				errx(1, "battery percentage is %s: %s", errstr,
 				    optarg);
 			break;
 		case 'z':
 			autoaction = AUTO_SUSPEND;
 			autolimit = strtonum(optarg, 1, 100, &errstr);
 			if (errstr != NULL)
-				errc(1, EINVAL, "%s percentage: %s", errstr,
+				errx(1, "battery percentage is %s: %s", errstr,
 				    optarg);
 			break;
 		case '?':