With the introduction of intra-column scrolling, the
scroll coordinates message was enhanced to give some
hint of positioning within a scrolled column.
Rather than rebuild this somewhat costly string from
scratch with each frame, we'll now do the bulk of the
work only when column headers are constructed.
The only remaining per frame costs will then be the
addition of a few terminfo escapes and the current
Frame_maxtask count.
Signed-off-by: Jim Warner <james.warner@comcast.net>