Assign deo->target a copy of target instead of target itself because
delayed_goto_uri_frame frees deo->target and SpiderMonkey owns target.
Reported by Jonas.
The two copies of delayed_open in src/ecmascript/spidermonkey/window.c
and in src/ecmascript/see/window.c are identical, so move them
to src/terminal/tab.c and eliminate the duplication.
Until the last change in src/ecmascript/see/window.c, the two copies
of delayed_goto_uri_frame in src/ecmascript/spidermonkey/window.c and
in src/ecmascript/see/window.c were identical. That change applies to
both versions, so move the newer one to src/session/task.c and eliminate
the duplication. Also move struct delayed_open to src/session/session.h.
