[Python-3000] PEP-3125 -- remove backslash continuation

[Tim Peters]

...

[Guido]
> I am worried that (as no indent is required on the next line) it will
> accidentally introduce legal interpretations for certain common (?)
> typos, e.g.
>
>   x = y+    # Used to be y+1, the 1 got dropped
>   f(x)

The Icon language also uses this rule, and I never experienced
problems with it there.

OTOH, the "open bracket" rule is certainly sufficient by itself, and
is invaluable for writing "big" list, tuple, and dict literals (things
I doubt come up in Andrew's EFL inspiration).