Difficult to get out the completions window

[Lennart Borgman]

It is quite difficult to close the completion window once you have 
entered it (with M-v for example). I suggest the following behaviour 
when focus is in the completion window:

1) On C-g close the completion window and move back to the minibuffer. 
This is what happens if you type ESC ESC ESC which runs 
delete-completion-window.

2) If the completion window is closed with C-x 0 then move back to the 
minibuffer.

BTW nothing is said in the Emacs manual "(emacs) Completion Commands" 
about how to get out of the completion window.