Network game works (at least sometimes).
Avoid server crash: minimized number of messages to send by:
- sending the messages more often (also gives smoother game play).
- clearing all message after each sending (avoids a lot of bugs).

Note: There are still a lot of critical bugs during network gaming.
Network game: Added proper client support for helicopters.
Also minor clean up.
Throw an error on unloadable map mesh
Added experimental 'caves' map

Uses a mesh instead of a heightmap
The heightmap is still hiding below the mesh
Network game: Added the code again for NetServerSeqPred.
Work in progress.
Commented out the NetServerSeqPred, since it does not work.
Disabled and added debug print outs.
Network game: Old server messages handled properly.
The problem was an incomplete copy constuctor for NetMsg,
this made the sequence number invalid.
Network game: Client should also handle old packages properly.
If server has too many messages, delete all (not great, but better than crash).
Check if we just received ACK message before sending.
Pre-check final packet length, so we don't corrupt the memory.
Disabled most of the debug print outs.
Removed missed debug print out and flush debug output buffers.
Network game: Send a quit message from client to server.
'NetServer::handleQuit' was not correctly mapped.
Network game: Moved the removal of old messages to after sending as it was before.
Improved the memory releasing.
Server: Set known client sequence number when client is created.
Move heightmap class into it's own file
Removed broken weapon class 'borer'

It was for heightmap modification, but it didn't actually work
Refactored all the heightmap bits out of the 'Map' class
Further cleanup of heightmap class
Network game: Allow UDP packages to be upto two times larger than MTU.
In most cases the packages are smaller than MTU. But when needed we allow
the package size to be larger than MTU, even if this leads to more package fragmentations
and therefore higher risk of packet loss.

Server: If the packet size is too large, shut down the server and the game.
Two minor dialog fixes.
Game Engine: Do not allow duplicates of the same dialog.
Net Client: 'Release' mouse if dialog opens.
Further separation of heightmap from map class
Move MapReg and MapRegistry classes into their own file

So a change to the Map class doesn't trigger such a massive recompile
Also, it's more correct this way
Removed heightmap from 'caves' map

This breaks the map from loading at the moment
Added support for multiple heightmaps

This includes support for no heightmap at all.
You'll probably want a mesh or two in that case.