Two new configuration options are added:
     - "enable_ipv6" to enable/disable the overall use of IPv6
     - "ipv6_server" to enable/disable the use of IPv6 sockets when running
       a server (when "enable_ipv6" is enabled)

Now Environment::clearAllObjects() unloads unused blocks in an interval
defined by max_clearobjects_extra_loaded_blocks (default 4096).

Also add a menuheader, menusplash, menufooter_clouds, and allow HD menu footers.
And finally don't git-ignore textures/base/.

If USE_CURL is set, it also downloads a list from a remote server.
The url of this list is configurable in minetest.conf using the setting "serverlist_url"
The local list of favorite servers is saved in client/serverlist/filename
filename is also configureable using the setting "serverlist_file"

Can be turned off in the key change GUI or in minetest.conf via doubletab_space

Configure using repeat_rightclick_time in minetest.conf

"aux1_descends" setting switches to the old descend control.