X11 map scrolling behavior [from Steve VanDevender]

X11 map scrolling behavior [from Steve VanDevender]
This isn't really a bug, but I find it does make the map scrolling in
the generic X11 version a lot less distracting.  The original behavior
produces certain boundaries where, when the cursor moves back and forth
across that boundary, the map scrolls with each crossing.  This is
particularly annoying in places like Sokoban where the player makes that
kind of movement frequently causing large jumps of the map each time.
Changing the border and delta constants in winmap.c as below eliminates
that behavior, as well as making the cursor easier to track by tending
to recenter it whenever the map shifts.