Change in behaviour of delete-frame v24.5/v25.1.

[Lars-Johan Liman]

Hi!

Platform: macOS, emacsformacosx 25.1 and 24.5 (for comparison).

How can I prevent Emacs v.25 from raising (de-iconifying) an iconified
frame when I delete the last visible frame?

Here's the chain of events to repeat it:

1) Fire up emacs v.25 (or v.24 for comparison). A 1st frame appears.

2) Find any file (C-x C-f) using the 1st frame.

3) Find a 2nd file and put it in a 2nd frame (C-x 5 f).

4) Iconify this 2nd frame (C-x C-z).

5) Go back to the 1st frame and delete it (C-x 5 0).

6a) If you're running Emacs v.25, the 2nd frame springs to life from its
    iconified state.

6b) If you're running Emacs v.24 the 2nd frame stays iconified (= what I
    want).

How do I prevent 6a) from happening when using Emacs v.25?

                                Best regards and thanks in advance,
                                  /Lars-Johan Liman
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