split() loses final part if it’s empty

[danielparks]

I ran into a few bugs:

Regex	Text	Limit	Expected	Actual	Notes
"-"	"a"	none	["a"]	["a"]
"-"	"a-"	none	["a", ""]	["a"]	incorrect
"-"	"a--"	none	["a", "", ""]	["a", ""]	incorrect
"-"	"a"	2	["a"]	["a", ""]	#521
"-"	"a-"	2	["a", ""]	["a", ""]
"-"	"a--"	2	["a", "-"]	["a", "-"]

See also #521: splitn incorrectly returns a trailing "" if there is one fewer part than the limit.

[danielparks]

I’ve already written tests; I should have a PR ready in the next couple of days.