Fix the memory allocation for the thresholds data

Allocate the appropriate amount of memory for storing the thresholds
data.  Before, we allocated the amount of memory required for storing a
_pointer_ to the thresholds data.  This crashed (at least) check_mysql
when using its "-S" option on FreeBSD/amd64 (as reported and analyzed by
Nikita Kalabukhov - 2797757).

Signed-off-by: Holger Weiss <holger@zedat.fu-berlin.de>

THANKS.in

@@ -254,3 +254,4 @@ Ben Timby
 Martin Foster
 Joe Presbrey
 Will Preston
+Nikita Kalabukhov

lib/utils_base.c

@@ -101,7 +101,9 @@ _set_thresholds(thresholds **my_thresholds, char *warn_string, char *critical_st
 {
 	thresholds *temp_thresholds = NULL;
 
-	temp_thresholds = malloc(sizeof(temp_thresholds));
+	if ((temp_thresholds = malloc(sizeof(thresholds))) == NULL)
+		die(STATE_UNKNOWN, _("Cannot allocate memory: %s\n"),
+		    strerror(errno));
 
 	temp_thresholds->warning = NULL;
 	temp_thresholds->critical = NULL;