Fix double indentation in _PrettyPrinterBase.group().

_PrettyPrinterBase.group() was increasing the indentation twice
(once in the call to begin_group() and once in the call to indent()).
Fixed by removing the call to indent().

IPython/lib/pretty.py

@@ -155,8 +155,7 b' class _PrettyPrinterBase(object):'
         """like begin_group / end_group but for the with statement."""
         self.begin_group(indent, open)
         try:
-            with self.indent(indent):
-                yield
+            yield
         finally:
             self.end_group(indent, close)