%cd: do not add same dir to dhist twice in a row

IPython/Magic.py

@@ -2670,6 +2670,7 b' Defaulting color scheme to \'NoColor\'"""'
         parameter_s = parameter_s.strip()
         #bkms = self.shell.persist.get("bookmarks",{})
 
+        oldcwd = os.getcwd()
         numcd = re.match(r'(-)(\d+)$',parameter_s)
         # jump in directory history by number
         if numcd:
@@ -2719,6 +2720,7 b' Defaulting color scheme to \'NoColor\'"""'
             else:
                 cwd = os.getcwd()
                 dhist = self.shell.user_ns['_dh']
+                if oldcwd != cwd:
                 dhist.append(cwd)
                 self.db['dhist'] = compress_dhist(dhist)[-100:]
                 
@@ -2728,6 +2730,8 b' Defaulting color scheme to \'NoColor\'"""'
                 platutils.set_term_title("IPy ~")
             cwd = os.getcwd()
             dhist = self.shell.user_ns['_dh']
+            
+            if oldcwd != cwd:
             dhist.append(cwd)
             self.db['dhist'] = compress_dhist(dhist)[-100:]
         if not 'q' in opts and self.shell.user_ns['_dh']: