Adds p.break_ for explicit newlines in lib.pretty

p.break_() explicitly includes a newline while pretty printing, and maintains indentation.
A simple test is included to show this working.

IPython/lib/pretty.py

@@ -230,6 +230,16 b' class PrettyPrinter(_PrettyPrinterBase):'
             self.buffer_width += width
             self._break_outer_groups()
 
+    def break_(self):
+        """
+        Explicitly insert a newline into the output, maintaining correct indentation.
+        """
+        self.flush()
+        self.output.write(self.newline)
+        self.output.write(' ' * self.indentation)
+        self.output_width = self.indentation
+        self.buffer_width = 0
+        
 
     def begin_group(self, indent=0, open=''):
         """

IPython/lib/tests/test_pretty.py

@@ -58,6 +58,13 b' class NoModule(object):'
 
 NoModule.__module__ = None
 
+class Breaking(object):
+    def _repr_pretty_(self, p, cycle):
+        with p.group(4,"TG: ",":"):
+            p.text("Breaking(")
+            p.break_()
+            p.text(")")
+
 
 def test_indentation():
     """Test correct indentation in groups"""
@@ -118,3 +125,11 b' def test_pprint_nomod():'
     """
     output = pretty.pretty(NoModule)
     nt.assert_equal(output, 'NoModule')
+    
+def test_pprint_break():
+    """
+    Test that p.break_ produces expected output
+    """
+    output = pretty.pretty(Breaking())
+    expected = "TG: Breaking(\n    ):"
+    nt.assert_equal(output, expected)