Prevent creating parent-less dialogs

[alsroot]

After moving to metacity we have many issues due to the fact that activity authors do not pass parent while creating ObjectChooser object(for example).

It could be useful for ObjectChooser to make parent argument required(it could be None) for 0.88 and add deprecation warning for 0.86 or do some smart job to autoset parent on shell side.

Also parent argument could be required for sugar.graphics.Window(w/ warning in 0.86) or new Dialog class.

[alsroot]

Shanged type to defect since parent-less dialogs are bugs for 0.86.

[alsroot]

Milestone to 0.88, since we are in code freeze

[tomeu]

I agree on this, but would be an API change so needs to be done at the start of a release cycle so activities have time to adapt. do people agree?