Switch default IPython directory back to ~/.ipython

As discussed at the dev meeting, we care more about a consistent default
across platforms than half-heartedly following the XDG specs.

IPython/utils/path.py

@@ -273,7 +273,6 b' def get_ipython_dir():'
 
 
     ipdir_def = '.ipython'
-    xdg_def = 'ipython'
 
     home_dir = get_home_dir()
     xdg_dir = get_xdg_dir()
@@ -284,20 +283,21 b' def get_ipython_dir():'
                       'Please use IPYTHONDIR instead.')
     ipdir = env.get('IPYTHONDIR', env.get('IPYTHON_DIR', None))
     if ipdir is None:
-        # not set explicitly, use XDG_CONFIG_HOME or HOME
-        home_ipdir = pjoin(home_dir, ipdir_def)
+        # not set explicitly, use ~/.ipython
+        ipdir = pjoin(home_dir, ipdir_def)
         if xdg_dir:
-            # use XDG, as long as the user isn't already
-            # using $HOME/.ipython and *not* XDG/ipython
-
-            xdg_ipdir = pjoin(xdg_dir, xdg_def)
-
-            if _writable_dir(xdg_ipdir) or not _writable_dir(home_ipdir):
-                ipdir = xdg_ipdir
-
-        if ipdir is None:
-            # not using XDG
-            ipdir = home_ipdir
+            # Several IPython versions (up to 1.x) defaulted to .config/ipython
+            # on Linux. We have decided to go back to using .ipython everywhere
+            xdg_ipdir = pjoin(xdg_dir, 'ipython')
+
+            if _writable_dir(xdg_ipdir):
+                cu = compress_user
+                if os.path.exists(ipdir):
+                    warnings.warn(('Ignoring {0} in favour of {1}. Remove {0} '
+                    'to get rid of this message').format(cu(xdg_ipdir), cu(ipdir)))
+                else:
+                    warnings.warn('Moving {0} to {1}'.format(cu(xdg_ipdir), cu(ipdir)))
+                    os.rename(xdg_ipdir, ipdir)
 
     ipdir = os.path.normpath(os.path.expanduser(ipdir))