add ignore_old_config configurable

for users who still use multiple versions of IPython

closes gh-414

IPython/config/default/ipython_config.py

@@ -11,6 +11,10 b' c = get_config()'
 
 # c.Global.nosep = True
 
+# If you still use multiple versions of IPytho on the same machine,
+# set this to True to suppress warnings about old configuration files
+# c.Global.ignore_old_config = False
+
 # Set this to determine the detail of what is logged at startup.
 # The default is 30 and possible values are 0,10,20,30,40,50.
 # c.Global.log_level = 20

IPython/frontend/terminal/ipapp.py

@@ -635,7 +635,8 b' class IPythonApp(Application):'
                 self.shell.showtraceback()
 
     def start_app(self):
-        check_for_old_config(self.ipython_dir)
+        if not getattr(self.master_config.Global, 'ignore_old_config', False):
+            check_for_old_config(self.ipython_dir)
         if self.master_config.Global.interact:
             self.log.debug("Starting IPython's mainloop...")
             self.shell.mainloop()

IPython/utils/path.py

@@ -418,4 +418,6 b' def check_for_old_config(ipython_dir=None):'
             warn.warn("""Found old IPython config file %r.
     The IPython configuration system has changed as of 0.11, and this file will be ignored.
     See http://ipython.github.com/ipython-doc/dev/config for details on the new config system.
-    The current default config file is 'ipython_config.py'"""%f)
+    The current default config file is 'ipython_config.py', where you can suppress these
+    warnings with `Global.ignore_old_config = True`."""%f)
+