Make Connection::Receive return the data via a SharedBuffer reference, so the caller doesn't have to choose the right buffer size in advance.

Conflicts:

	src/test.cpp

Switch more stuff to use the logging thing and fix segfault on player leave from server as introduced in a previous switch-to-logging commit

Use the logger; also, default to not showing much crap in console. Use --info-on-stderr to enable crap.

strict_protocol_version_checking setting; PROTOCOL_VERSION in clientserver.h; clean up defaultsettings.cpp and minetest.conf.example