- Neatly placed all emerge related code into a new file, emerge.cpp
- Greatly cleaned up the code in EmergeThread::Thread()
- Reworked Emerge queue.  Now an actual std::queue of v3s16 block positions
- Removed the completely unnecessary map of peer ids requesting blocks

liquid_kind was declared as an u8, but used to hold a content_t value, which is delcared to be a u16.

changing this fixes (at least for me) the problem reported in bug #414.

- Don't select blocks for drawing in every frame
- Sort meshbuffers by material before drawing