#64 Point jumps to end of line if line is almost as long as there are cols and there is a tab char

If a line contains a tab character and roughly has the same number of characters (whether combined UTF-8 or not) as there are window columns (curwp->w_cols) then the point will jump to the column of `curwp->w_cols - 3`, where _3_ is the extra length added by the tab character. One jumped to that new position, you can't use move up until you jump to the beginning of the line or move down a line. My guess is that it has something to do with the `display` function in `display.c`