Don't permit to open inventory is playerCAO isn't present. This prevent to open an empty inventory at player load. ok @zeno-

* Increase performance (client)
* Avoid changing a global value to solve a local problem

This reverts commit d25ff8fd.

* Increase performance (client)
* Avoid changing a global value to solve a local problem

Minetest fails to build on GNU/Hurd due to a name clash with OSX/Apple,
both are defining the __MACH__ keyword. This commit fixes the issue.

Before patch, function consumes up to ~8% of the main server loop. After, ~0% (below level of 2 places of significance)

Also simplify wget steps and apt-get install zlib1g-dev libjsoncpp-dev

* Move networkcode to a dedicated directory
* Rename clientserver.h to network/networkprotocol.h (Better name) and sanitize some includes
* Create object NetworkPacket
  * It stores command (opcode) and data separated
  * It also stores peer_id
  * Data reading can be done by using a streaming interface
* Change packet routing analysis
  * Remove old conditional analysis
  * Now uses function pointed analysis and add connection state ({Client,Server}::handlers)
  * Connection state permit to categorize condition to handle before analyze packets
  * Create a handler for depreciated messages, instead of duplicating code

Conf.example: Add mgv7 cave1, cave2 noiseparams
Mgv7: Make skipping of mountain code relative to y=0 not water level
Mountain noise offset now -0.6 to compensate
Tune chance of large caves

Remove software exception translator function, simplifying exception handler
macros.  FatalSystemExceptions are left unhandled.

Remove inventorycube() workaround for default:glass in minimal game

Disables local map saving for all local server types

See: https://github.com/minetest/minetest/issues/2024

This fixes issue #2219

When SER_FMT_VER_LOWEST is set to zero, then the test is stupid in INIT because all client works. In mapblock we check if client's serialization version is < 24, but if client sent serialization version < 24 (15 for example) the server set it and tried to send nodes, then BOOM

To resolve the problem:
* Create a different CLIENT_MIN_VERSION to handle this problem
* Remove the exception
* Use an assert in case of bad developer code