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

utility.h: Change Buffer's interface to be more compatible with SharedBuffer's interface, connection.h: use Buffer instead of SharedBuffer in command and event queues

Add new Connection test in test.cpp in case needed in the future (commented out), improve comments in test.cpp a bit

Fix flowing liquid spacing; water and lava next to each other will glitch a bit but it isn't as bad as this was

occlusion culling fix, a little reshaping of map rendering for more useful profiler output and dynamic profiler text size

Default max_simultaneous_block_sends_server_total to 2 to make network not cough too much on the fixed block sending code