Added support for --cpu-priority for OS X.

src/Platform_mac.cpp

@@ -23,6 +23,7 @@
 
 
 #include <stdlib.h>
+#include <sys/resource.h>
 #include <uv.h>
 
 
@@ -61,6 +62,37 @@ void Platform::setProcessPriority(int priority)
 
 void Platform::setThreadPriority(int priority)
 {
+    if (priority == -1) {
+        return;
+    }
 
+    int prio = 19;
+    switch (priority)
+    {
+    case 1:
+        prio = 5;
+        break;
+
+    case 2:
+        prio = 0;
+        break;
+
+    case 3:
+        prio = -5;
+        break;
+
+    case 4:
+        prio = -10;
+        break;
+
+    case 5:
+        prio = -15;
+        break;
+
+    default:
+        break;
+    }
+
+    setpriority(PRIO_PROCESS, 0, prio);
 }