Current goal column for vertical motion.
It is the column where point was at the start of the current run
of vertical motion commands.
When moving by visual lines via `line-move-visual', it is a cons
cell (COL . HSCROLL), where COL is the x-position, in pixels,
divided by the default column width, and HSCROLL is the number of
columns by which window is scrolled from left margin.
When the `track-eol' feature is doing its job, the value is
`most-positive-fixnum'.