don't crash apps on TraitErrors when parsing command-line

IPython/config/application.py

@@ -31,7 +31,7 b' from IPython.config.loader import ('
 )
 
 from IPython.utils.traitlets import (
-    Unicode, List, Int, Enum, Dict, Instance
+    Unicode, List, Int, Enum, Dict, Instance, TraitError
 )
 from IPython.utils.importstring import import_item
 from IPython.utils.text import indent, wrap_paragraphs, dedent
@@ -326,12 +326,12 b' class Application(SingletonConfigurable):'
                                         flags=self.flags)
         try:
             config = loader.load_config()
-        except ArgumentError as e:
-            self.log.fatal(str(e))
+            self.update_config(config)
+        except (TraitError, ArgumentError) as e:
             self.print_description()
             self.print_help()
+            self.log.fatal(str(e))
             self.exit(1)
-        self.update_config(config)
         # store unparsed args in extra_args
         self.extra_args = loader.extra_args
 

IPython/core/application.py

@@ -277,8 +277,9 b' class BaseIPythonApplication(Application):'
         
     
     def initialize(self, argv=None):
-        self.init_crash_handler()
+        # don't hook up crash handler before parsing command-line
         self.parse_command_line(argv)
+        self.init_crash_handler()
         if self.subapp is not None:
             # stop here if subapp is taking over
             return