Partial custom fields design document

[Joel Peshkin]

Mark Davis wrote:

> While we're talking about this, I'd like to see a way to mark certain 
> fields as required at certain points.
>
> Just as there is a required comment to mark a bug fixed now, I'd like 
> to require that a user add a changeset number...
>
> ew... that just got ugly didn't it?
>
Rather than burdening customfields with this, perhaps an approach 
similar to the CheckCanChangeField() function in process_bug would 
help.  Essentially, you could put such checks in a known and reasonably 
stable location in the code.  Would that suffice?