Ensure compat data is saved

[koopersmith]

Two things for compat:

1) Some plugins were expecting compat to be rendered and saved when an image is uploaded (for things like default values of form elements). As a result, when an image is first uploaded, should we fire saveCompat?

2) The compat view should have the same save-on-removal features the attachment details have. Patch attached for that.

Test this by opening up the edit gallery view, selecting an image, and inputting some data into a compat field. While the field is still active, click on another attachment. Did the data save?

Original support thread that prompted part 1: ​http://wordpress.org/support/topic/doesnt-save-custom-field-selectbox-data-in-media-frame?replies=2

I don't know if we should do anything about this.

Replying to nacin:

I don't know if we should do anything about this.

I meant for part 1.

+1 for part 2.

In 23098:

Media: When the attachment details view changes to another view or attachment, save compat fields on destroy. (We already do this for non-compat fields.) props koopersmith. fixes #22776.

Replying to nacin:

I don't know if we should do anything about this.

I meant for part 1. Part 2 is in.

Replying to nacin:

Replying to nacin:

I don't know if we should do anything about this.

I meant for part 1. Part 2 is in.

Oops, back button caused me to post that twice. Or I'm just tried. That.

Agreed. For part 1, it's bad any way you slice it — the bottom line is that we'd have fire an ajax request any time we encounter an attachment for either render and/or insert — and all this just to provide safety for not providing default values, which is a poor development practice in its own right (regardless of the version of WordPress that you run). We're going to let part 1 ride.