install_extension always returns the path to the installed file.

IPython/core/extensions.py

@@ -133,6 +133,8 b' class ExtensionManager(Configurable):'
         If filename is given, the file will be so named (inside the extension
         directory). Otherwise, the name from the URL will be used. The file must
         have a .py or .zip extension; otherwise, a ValueError will be raised.
+        
+        Returns the full path to the installed file.
         """
         # Ensure the extension directory exists
         if not os.path.isdir(self.ipython_extension_dir):
@@ -151,4 +153,5 b' class ExtensionManager(Configurable):'
             raise ValueError("The file must have a .py or .zip extension", filename)
         
         filename = os.path.join(self.ipython_extension_dir, filename)
-        return copy(url, filename)
+        copy(url, filename)
+        return filename

IPython/core/magic.py

@@ -3456,7 +3456,7 b' Defaulting color scheme to \'NoColor\'"""'
         """
         opts, args = self.parse_options(parameter_s, 'n:')
         try:
-            filename, headers = self.extension_manager.install_extension(args, opts.get('n'))
+            filename = self.extension_manager.install_extension(args, opts.get('n'))
         except ValueError as e:
             print e
             return