experiment: support out-of-bounds indices in cut

http://arclanguage.org/item?id=18451
move split to arc.arc

I'm trying to eliminate halve.
just trash all date/time input processing in forms

Not currently used anywhere so I have no friggin' idea what valid values are,
etc. Can always bring back if needed, in which case we'll know enough to write
a test.
drop litmatch and make endmatch a function

Why were they defined as macros? For performance?
string tests aren't old style anymore
again forgot to run old tests