Name attribute problems in <form>

[Alfonso Martínez de Lizarrondo]

1. Load replace by class sample in any browser
2. Insert a form and set name=f1, close the dialog
3. Switch to source, it's OK
4. Switch to design and using the toolbar button edit the form (as it doesn't have any content the context menu might not work, toolbar button is easier)
5. Change the name to f2, close the dialog
6. Switch to source, now the name is duplicated:

   <form method="get" name="f1" name="f2">
   

7. when you switch back to design the name=f2 is lost.

[Artur Formella]

Fixed with [3597] (as part of #3631).