Check whether AJAX is generally broken with enctype="multipart/form-data"

[stephanrauh]

This is a follow-up of #734. We need to check if AJAX is broken for every form widget if the form encoding is set to enctype="multipart/form-data".

[stephanrauh]

It seems to be OK with input fields.

[stephanrauh]

A quick survey reveals three suspicious decode() methods:

• NavLinkRenderer
• Poll
• Checkbox (only the hidden state attribute is affected)

[stephanrauh]

The three components work with AJAX and enctype="multipart/form-data". Maybe the topic pops up later again, but I'll close the issue for the moment.