fix %edit foo for interactively defined variables

Effectively handles cases such as:

    In [1]: def foo(): return 5
    In [2]: %edit foo

Where `%edit foo` effectively turns into `%edit 1` by parsing the `<ipython-input-NN-…>` fake filename.

IPython/core/magics/code.py

@@ -17,6 +17,7 b' import inspect'
 import io
 import json
 import os
+import re
 import sys
 from urllib2 import urlopen
 
@@ -39,6 +40,13 b' from IPython.utils.warn import warn'
 # Used for exception handling in magic_edit
 class MacroToEdit(ValueError): pass
 
+ipython_input_pat = re.compile(r"<ipython\-input\-(\d+)-[a-z\d]+>$")
+
+class InteractivelyDefined(Exception):
+    """Exception for interactively defined variable in magic_edit"""
+    def __init__(self, index):
+        self.index = index
+
 
 @magics_class
 class CodeMagics(Magics):
@@ -302,6 +310,10 b' class CodeMagics(Magics):'
                                     data = attr
                                     break
 
+                        m = ipython_input_pat.match(os.path.basename(filename))
+                        if m:
+                            raise InteractivelyDefined(int(m.groups()[0]))
+                        
                         datafile = 1
                     if filename is None:
                         filename = make_filename(args)
@@ -491,6 +503,11 b' class CodeMagics(Magics):'
         except MacroToEdit as e:
             self._edit_macro(args, e.args[0])
             return
+        except InteractivelyDefined as e:
+            print "Editing In[%i]" % e.index
+            args = str(e.index)
+            filename, lineno, is_temp = self._find_edit_target(self.shell, 
+                                                       args, opts, last_call)
 
         # do actual editing here
         print 'Editing...',