Aesthetics: off-by-one in line drawing

Aesthetics: off-by-one in line drawing

It is a general problem when doing graphics to know where a line
begins and where it ends pixel-wise. At the instigation of Scott, and
with the use of the kmag magnifier, this commit corrects 3 areas:

* foreign marks were larger than the row element they were supposed to
  mark. This could lead to moving lines, depending on paint ordering.

* visible spaces were drawn outside of their box (select a single
  space to see this).

* the `L' blinking caret would leave a cursor dropping because the
  horizontal part was too wide.