Search for printers on address given by user using CUPS's SNMP backend.
This modification typically finds network printers publishing themselves
on port 9100.
Check successful installation of new printer by search
in list of destinations given by CUPS. Add index to the end
of name of new printer if the name is already used.
Pass a GCancellable object to g_dbus_proxy_call() for DevicesGet
method. This assures that g-c-c won't crash when user cancels addition
of new printer before the call is finished (rhbz#691931).
This patch makes PpNewPrinterDialog to call DevicesGet method
asynchronously now.
It also adds spinner to the lower left corner with label showing
status of this operation (#644212).
The dialog is able to add printers discovered by cupsGetDevices().
It can also add printers from a remote CUPS server by typing
its address and selecting printer we want to add (#640734).
