Use the most recent window to make quickfix jumps

[qstrahl]

It always bothered me that the default vim behaviour was to use whatever unrelated window lay at the bottom of the screen to make quickfix jumps. This small patch changes that behaviour so that your first jump after running a quickfix command leaves you in the same window, and furthermore, if you do something like copen to navigate the quickfix window, pressing <Return> will jump you back in the previous window.

[qstrahl]

@romainl I've gone ahead and found a different, cleaner approach