Add skip_doctest decorator for magic_install_default_config.

Closes gh-467

IPython/core/magic.py

@@ -3360,6 +3360,7 b' Defaulting color scheme to \'NoColor\'"""'
                 shutil.copy(src, dst)
                 print "    %s" % f
 
+    @skip_doctest
     def magic_install_default_config(self, s):
         """Install IPython's default config file into the .ipython dir.