add a threading compatibility shim - likely cleaner ways of doing this but we…

add a threading compatibility shim - likely cleaner ways of doing this but we don't want to depend on boost threads unless we really have to for now

src/threading.h

+#ifndef NODE_SQLITE3_SRC_THREADING_H
+#define NODE_SQLITE3_SRC_THREADING_H
+
+
+#if defined(NODE_SQLITE3_BOOST_THREADING)
+
+#include <boost/thread/mutex.hpp>
+    
+    #define NODE_SQLITE3_MUTEX_t boost::mutex mutex;
+         
+    #define NODE_SQLITE3_MUTEX_INIT 
+
+    #define NODE_SQLITE3_MUTEX_LOCK(m) (*m).lock();
+    
+    #define NODE_SQLITE3_MUTEX_UNLOCK(m) (*m).unlock();
+  
+    #define NODE_SQLITE3_MUTEX_DESTROY mutex.unlock();
+
+#else
+
+    #define NODE_SQLITE3_MUTEX_t pthread_mutex_t mutex;
+    
+    #define NODE_SQLITE3_MUTEX_INIT pthread_mutex_init(&mutex,NULL);
+        
+    #define NODE_SQLITE3_MUTEX_LOCK(m) pthread_mutex_lock(m);
+    
+    #define NODE_SQLITE3_MUTEX_UNLOCK(m) pthread_mutex_unlock(m);
+    
+    #define NODE_SQLITE3_MUTEX_DESTROY pthread_mutex_destroy(&mutex);
+
+#endif
+
+
+#endif // NODE_SQLITE3_SRC_THREADING_H
\ No newline at end of file