README.Debian: improved Apache2 and Nginx setup instructions (Closes: #740734)

 Thanks to Harald Dunkel.
added "snmp-mibs-downloader" to Suggests of server packages (Closes: #740815)
control: correcting accidentally uncommented line
zabbix-agent: Depends: +pciutils; Recommends: +usbutils (Closes: #744385)

 "pciutils" and "usbutils" are needed for "system.hw.devices[pci]" (default)
 and for "system.hw.devices[usb]", accordingly.

 Assoicated errors (printed to STDERR):

    sh: 1: lspci: not found
    sh: 1: lsusb: not found

 Test:

    /usr/sbin/zabbix_agentd -t system.hw.devices[pci]
    /usr/sbin/zabbix_agentd -t system.hw.devices[usb]

 Thanks, Harald Dunkel.
Zabbix 2.2.4 - Squeeze

  * New upstream release