Clean up threading

* Rename everything.
    * Strip J prefix.
    * Change UpperCamelCase functions to lowerCamelCase.
  * Remove global (!) semaphore count mutex on OSX.
  * Remove semaphore count getter (unused, unsafe, depended on internal
    API functions on Windows, and used a hack on OSX).
  * Add `Atomic<type>`.
  * Make `Thread` handle thread names.
  * Add support for C++11 multi-threading.
  * Combine pthread and win32 sources.
  * Remove `ThreadStarted` (unused, unneeded).
  * Move some includes from the headers to the sources.
  * Move all of `Event` into its header (allows inlining with no new includes).
  * Make `Event` use `Semaphore` (except on Windows).
  * Move some porting functions into `Thread`.
  * Integrate logging with `Thread`.
  * Add threading test.

src/player.h

@@ -23,7 +23,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "irrlichttypes_bloated.h"
 #include "inventory.h"
 #include "constants.h" // BS
-#include "jthread/jmutex.h"
+#include "threading/mutex.h"
 #include <list>
 
 #define PLAYERNAME_SIZE 20
@@ -413,7 +413,7 @@ private:
 	// Protect some critical areas
 	// hud for example can be modified by EmergeThread
 	// and ServerThread
-	JMutex m_mutex;
+	Mutex m_mutex;
 };