Add ability to exclude fields differently when the ticket is being created vs edited

[jvetter@…]

I would like the ability to exclude ticket fields when a ticket is created, but have the field be available when tickets are being edited.

For example, I have a custom field called percent_complete that I would like to be hidden during creation and defaulted to 0. Then when the ticket is edited, I would like the field to be available to be changed so the owner can provide completion information.