add the ability to set the priority of the render process as commandline argument

src/com/sheepit/client/standalone/Worker.java

@@ -91,6 +91,9 @@ public class Worker {
 	@Option(name = "--no-systray", usage = "Don't use systray", required = false)
 	private boolean no_systray = false;
 	
+	@Option(name = "-priority", usage = "Set render process priority (19 lowest to -19 highest)", required = false)
+	private int priority = 19;
+	
 	public static void main(String[] args) {
 		new Worker().doMain(args);
 	}
@@ -112,6 +115,7 @@ public class Worker {
 		ComputeType compute_method = ComputeType.CPU;
 		Configuration config = new Configuration(null, login, password);
 		config.setPrintLog(print_log);
+		config.setUsePriority(priority);
 		
 		if (cache_dir != null) {
 			File a_dir = new File(cache_dir);