This option fixes the fact that the following two lines sometimes
place the variables in different scopes at the top-level of included
scripts:
var x = 1;
y = 2;

I plan to use this to experiment on if this is what's causing much
of the remaining scope chain weirdness... it certain explains some
things we've been seeing (and possibly even things like the METHODJIT
issues DigitalMan saw yesterday).

Enabling in sbbs/jsexec is a much bigger lift, but this change may
end up being all upside... the docs have suggested this option always
be set since it was originally introduced, and now that I understand
scopes better, it's pretty clear why that is.