split-string behavior change

[Drew Adams]

I'm not suggesting we change anything now, but I'm curious about the change
in behavior of split-string from Emacs 21 to 22.

Emacs 20, 21: (split-string "abc" "") gives ("a" "b" "c")

Emacs 22: (split-string "abc" "")   gives ("" "a" "b" "c" "")
     and: (split-string "abc" "" t) gives ("a" "b" "c")

IOW, we added an optional third arg, for which the non-nil value - not the
nil value, gives the same result as before. And using the same code as
before, with no third arg, now gives a different result (breaks).

That seems backward, to me. Why wasn't the polarity of the new OMIT-NULLS
arg reversed (and so called INCLUDE-NULLS)?

If this change was a mistake, so be it. But if it was conscious decision and
not a mistake, then I'm curious to know the reason for it.