Die properly in case of non-existent plugin

include/gmon.py

 
     def _load_plugin(self, pluginpath):
         modpath = "%s/%s.py" % (pluginpath, self.name)
-        with open(modpath) as fh:
-            module = imp.load_module(self.name, fh, modpath,
-                                     (".py", "r", imp.PY_SOURCE))
+        try:
+            with open(modpath) as fh:
+                module = imp.load_module(self.name, fh, modpath,
+                                         (".py", "r", imp.PY_SOURCE))
+        except IOError:
+            raise GmonPluginError(self.name)
         self.plugin = module.Plugin(self.plugindata)
 
     def _format_output(self, raw):
 
     def __init__(self, cmdargs):
         self._set_pluginpath()
-        self.subcommand = Subcommand(cmdargs, self.pluginpath)
+        try:
+            self.subcommand = Subcommand(cmdargs, self.pluginpath)
+        except GmonPluginError as e:
+            self.die("no such plugin: %s" % e)
 
     def _set_pluginpath(self):
         mypath = os.path.dirname(os.path.realpath(sys.argv[0]))