expanduser on %%file targets

closes  #2993

IPython/core/magics/osm.py

@@ -711,7 +711,7 b' class OSMagics(Magics):'
         For frontends that do not support stdin (Notebook), -f is implied.
         """
         args = magic_arguments.parse_argstring(self.file, line)
-        filename = unquote_filename(args.filename)
+        filename = os.path.expanduser(unquote_filename(args.filename))
         
         if os.path.exists(filename):
             if args.amend: