Sets form's target to `_blank` when submitted via Ctrl + Left Mouse Button or Ctrl + Enter.
As of
Useful for "saving" form state in preceding tab.
Ctrl+enter will work alike where plain enter would submit form (ie NOT on textareas).
Sadly, using middle mouse button for the same purpose does not work that well, because it would require invoking "artificial" form.submit(), what triggers popup blocker because form is "artificially dirty", ie got recently changed.
For reference, request for similar functionality in Firefox from 1999.
