Add message to warn the user if a form has too many fields.

Signed-off-by: Hugues Peccatte <hugues.peccatte@gmail.com>
Correct warning message.

Signed-off-by: Hugues Peccatte <hugues.peccatte@gmail.com>
Merge pull request #1119 from Tithugues/help4319

Add message to warn the user if a form has too many fields.