rename `%%file` to `%%fwrite`

keeps `%%file` as alias

Alternative to  #3313, no behavior is changed.

IPython/core/interactiveshell.py

@@ -2060,6 +2060,7 b' class InteractiveShell(SingletonConfigurable):'
         mman.register_alias('rep', 'recall')
         mman.register_alias('SVG', 'svg', 'cell')
         mman.register_alias('HTML', 'html', 'cell')
+        mman.register_alias('file', 'fwrite', 'cell')
 
         # FIXME: Move the color initialization to the DisplayHook, which
         # should be split into a prompt manager and displayhook. We probably

IPython/core/magics/osm.py

@@ -707,12 +707,12 b' class OSMagics(Magics):'
         help='file to write'
     )
     @cell_magic
-    def file(self, line, cell):
+    def fwrite(self, line, cell):
         """Write the contents of the cell to a file.
         
         The file will be overwritten unless the -a (--append) flag is specified.
         """
-        args = magic_arguments.parse_argstring(self.file, line)
+        args = magic_arguments.parse_argstring(self.fwrite, line)
         filename = os.path.expanduser(unquote_filename(args.filename))
         
         if os.path.exists(filename):