mintinstall.py: Use xapp for network proxy setup.

xapp.os.add_network_proxy_to_env() will set the environment so
that all network traffic (besides APT) is routed thru the configured
proxy.

mintinstall.py: Use xapp for network proxy setup.

xapp.os.add_network_proxy_to_env() will set the environment so
that all network traffic (besides APT) is routed thru the configured
proxy.

8.3.8

Update flatpak match data.

Update flatpak match info.