add config file inheritance to kernelapp

Add KernelApp.parent_appname configurable, which sets the default config file.  Frontends should specify this in the arguments they pass to kernels they start.

closes gh-544

IPython/frontend/qt/console/qtconsoleapp.py

@@ -292,7 +292,8 b' class IPythonQtConsoleApp(BaseIPythonApplication):'
             argv = sys.argv[1:]
 
         self.kernel_argv = list(argv) # copy
-
+        # kernel should inherit default config file from frontend
+        self.kernel_argv.append("KernelApp.parent_appname='%s'"%self.name)
         # scrub frontend-specific flags
         for a in argv:
             if a.startswith('--') and a[2:] in qt_flags:

IPython/zmq/kernelapp.py

@@ -82,7 +82,17 b' class KernelApp(BaseIPythonApplication):'
     heartbeat = Instance(Heartbeat)
     session = Instance('IPython.zmq.session.Session')
     ports = Dict()
-
+    
+    # inherit config file name from parent:
+    parent_appname = Unicode(config=True)
+    def _parent_appname_changed(self, name, old, new):
+        if self.config_file_specified:
+            # it was manually specified, ignore
+            return
+        self.config_file_name = new.replace('-','_') + u'_config.py'
+        # don't let this count as specifying the config file
+        self.config_file_specified = False
+        
     # connection info:
     ip = Unicode(LOCALHOST, config=True,
         help="Set the IP or interface on which the kernel will listen.")