init scripts need minor modification to be used 'as is' for FreeBSD 8.2

By default on FreeBSD 8.2 zabbix_server and zabbix_agentd are installed in /usr/local/sbin . To use the init scripts provided in zabbix/misc/init.d/freebsd I had to change the command variable in those scripts to look for the binaries in the sbin directory instead of the bin directory.