Add support for Android 2.3+

There have been plenty of ppl involved in creating this version.
I don't wanna mention names as I'm sure I'd forget someone so I
just tell where help has been done:
- The partial android versions done by various ppl
- Testing on different android devices
- reviewing code (especially the in core changes)
- testing controls
- reviewing texts

A big thank you to everyone helping this to be completed!

src/jthread/pthread/jsemaphore.cpp

@@ -51,7 +51,15 @@ JSemaphore::JSemaphore() {
 
 JSemaphore::~JSemaphore() {
 	int sem_destroy_retval = sem_destroy(&m_semaphore);
+#ifdef __ANDROID__
+// WORKAROUND for broken bionic semaphore implementation!
+	assert(
+			(sem_destroy_retval == 0) ||
+			(errno == EBUSY)
+		);
+#else
 	assert(sem_destroy_retval == 0);
+#endif
 	UNUSED(sem_destroy_retval);
 }
 

src/jthread/pthread/jthread.cpp

@@ -111,7 +111,11 @@ int JThread::Kill()
 		}
 		return ERR_JTHREAD_NOTRUNNING;
 	}
+#ifdef __ANDROID__
+	pthread_kill(threadid, SIGKILL);
+#else
 	pthread_cancel(threadid);
+#endif
 	if (started) {
 		int pthread_join_retval = pthread_join(threadid,&status);
 		assert(pthread_join_retval == 0);