handle errors when not adding a loaded component

src/jflow/workflow.py

@@ -111,6 +111,7 @@ class Workflow(threading.Thread):
     
     def add_component(self, component_name, args=[], kwargs={}, component_prefix="default"):
         # first build and check if this component is OK
+        if self.comp_pckg.has_key(component_name):
             my_pckge = __import__(self.comp_pckg[component_name], globals(), locals(), [component_name], -1)
             # build the object and define required field
             cmpt_object = getattr(my_pckge, component_name)()
@@ -134,6 +135,9 @@ class Workflow(threading.Thread):
 
             return cmpt_object
         
+        else:
+            sys.exit(component_name + " component cannot be loaded, available components are: " + ", ".join(self.comp_pckg.keys()))
+    
     def pre_process(self):
         pass