[monitoring-plugins] It's useful to use 'useful' instead of 'usefull'

[Jan Wagner]

 Module: monitoring-plugins
 Branch: master
 Commit: 1723a3c7610cc43438c51d1e5fed43e15099a60e
 Author: Jan Wagner <waja at cyconet.org>
   Date: Fri Nov 18 11:47:20 2016 +0100
    URL: https://www.monitoring-plugins.org/repositories/monitoring-plugins/commit/?id=1723a3c

It's useful to use 'useful' instead of 'usefull'

---

 plugins-scripts/check_ifoperstatus.pl | 2 +-
 plugins-scripts/check_ifstatus.pl     | 2 +-
 plugins/check_ntp_time.c              | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/plugins-scripts/check_ifoperstatus.pl b/plugins-scripts/check_ifoperstatus.pl
index 3eed4bc..9ede163 100755
--- a/plugins-scripts/check_ifoperstatus.pl
+++ b/plugins-scripts/check_ifoperstatus.pl
@@ -325,7 +325,7 @@ sub print_help() {
 	printf "                     (Implies the use of -I)\n";
 	printf "   -w (--warn =i|w|c) ignore|warn|crit if the interface is dormant (default critical)\n";
 	printf "   -D (--admin-down =i|w|c) same for administratively down interfaces (default warning)\n";
-	printf "   -M (--maxmsgsize) Max message size - usefull only for v1 or v2c\n";
+	printf "   -M (--maxmsgsize) Max message size - useful only for v1 or v2c\n";
 	printf "   -t (--timeout)    seconds before the plugin times out (default=$TIMEOUT)\n";
 	printf "   -V (--version)    Plugin version\n";
 	printf "   -h (--help)       usage help \n\n";
diff --git a/plugins-scripts/check_ifstatus.pl b/plugins-scripts/check_ifstatus.pl
index 9f2f7c3..32984e5 100755
--- a/plugins-scripts/check_ifstatus.pl
+++ b/plugins-scripts/check_ifstatus.pl
@@ -280,7 +280,7 @@ sub print_help() {
 	printf "                     in hex with 0x prefix generated by using \"snmpkey\" utility\n"; 
 	printf "                     privacy password and authEngineID\n";
 	printf "   -P (--privproto)  privacy protocol (DES or AES; default: DES)\n";
-	printf "   -M (--maxmsgsize) Max message size - usefull only for v1 or v2c\n";
+	printf "   -M (--maxmsgsize) Max message size - useful only for v1 or v2c\n";
 	printf "   -t (--timeout)    seconds before the plugin times out (default=$TIMEOUT)\n";
 	printf "   -V (--version)    Plugin version\n";
 	printf "   -h (--help)       usage help \n\n";
diff --git a/plugins/check_ntp_time.c b/plugins/check_ntp_time.c
index 1cc8cbf..391b2df 100644
--- a/plugins/check_ntp_time.c
+++ b/plugins/check_ntp_time.c
@@ -633,7 +633,7 @@ void print_help(void){
 	printf("%s\n", _("Notes:"));
 	printf(" %s\n", _("If you'd rather want to monitor an NTP server, please use"));
 	printf(" %s\n", _("check_ntp_peer."));
-	printf(" %s\n", _("--time-offset is usefull for compensating for servers with known"));
+	printf(" %s\n", _("--time-offset is useful for compensating for servers with known"));
 	printf(" %s\n", _("and expected clock skew."));
 	printf("\n");
 	printf(UT_THRESHOLDS_NOTES);