Dislike: shell opens in different window

[Tory S. Anderson]

Having recently switched to emacs v25, I notice that now (shell) uses 
(pop-to-buffer) rather than its former (pop-to-buffer-same-window) ~line 722 of 
shell.el. I very much dislike this change because I sometimes use complex and 
deliberate window setups, which are screwed up by this behavior. I changed it 
back on my system; is there a place I can find an explanation for this change? 
Also, is there a conventional way to find out in what version this change was 
made?