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/client/clientlauncher.cpp

@@ -651,14 +651,14 @@ void ClientLauncher::speed_tests()
 		infostream << "Around 5000/ms should do well here." << std::endl;
 		TimeTaker timer("Testing mutex speed");
 
-		JMutex m;
+		Mutex m;
 		u32 n = 0;
 		u32 i = 0;
 		do {
 			n += 10000;
 			for (; i < n; i++) {
-				m.Lock();
-				m.Unlock();
+				m.lock();
+				m.unlock();
 			}
 		}
 		// Do at least 10ms