Set minimum concurreny,

fix: call stop() if all tesks are processed

src/JobManager.js

@@ -40,6 +40,7 @@ JobManager.prototype.updateState = function(){
 };
 
 JobManager.prototype.setConcurrency = function( newVal ){
+    if( newVal > 1){
         if( newVal > this.tmpPoolLen ){
             var tmpPool = this.tmpPool;
             var additionalPoolBlocks = Math.ceil( ( newVal - this.tmpPoolLen )/this.workers.length ), i;
@@ -49,6 +50,7 @@ JobManager.prototype.setConcurrency = function( newVal ){
             this.tmpPoolLen += additionalPoolBlocks * this.workers.length ;
         }
         this.concurrency = newVal;
+    }
 };
 
 /*
@@ -73,7 +75,7 @@ JobManager.prototype.$doWork_ = function( cb ){
     var self = this;
     var task = self.tasks.splice(0, 1)[0];
     if( task == undefined ){
-        if( this.onStopped ){ this.onStopped(); }
+        this.stop();
     }
     var worker = self.getFromPool();
     this.work( task, worker, function(err){