tentative fix for python2.6

Author: 0x0L

pandas_datareader/famafrench.py

@@ -91,7 +91,7 @@ def _get_data(name):
         start = 0 if not match else match.start()
 
         df = read_csv(StringIO('Date' + src[start:]), **params)
-        try: df = df.to_period()
+        try: df = df.to_period(df.index.inferred_freq[:1])
         except: pass
         datasets[i] = df