Set number of columns WINDOW is scrolled from left margin to NCOL.
WINDOW must be a live window and defaults to the selected one.
Clip the number to a reasonable value if out of range.
Return the new number. NCOL should be zero or positive.
Note that if `automatic-hscrolling' is non-nil, you cannot scroll the
window so that the location of point moves off-window. (fn WINDOW NCOL)